Principles in the use of letters 'b', 'u' and 'v' in Early Modern English typography
Solution 1:
'V' and 'u' were regarded as the same letter from antiquity until well after this time. Some texts used only one form; some used both forms, but the choice was often either arbitrary, or based on something other than the sound (such as aesthetic reasons).
The letter you have identified as 'b' is not 'b': it is 'v' - it appears that in that text, the form with the ascender is used word-initially.
Solution 2:
During the late Middle Ages, two forms of 'v' developed, which were both used for its ancestor 'u' and modern 'v'. The pointed form 'v' was written at the beginning of a word, while a rounded form 'u' was used in the middle or end, regardless of sound. So whereas 'valor' and 'excuse' appeared as in modern printing, 'have' and 'upon' were printed 'haue' and 'vpon'. The first distinction between the letters 'u' and 'v' is recorded in a Gothic alphabet from 1386, where 'v' preceded 'u'. Printers eschewed capital 'U' into the 17th century and the distinction between the two letters was not fully accepted by the French Academy until 1762. Even today, jewellery brand BVLGARI uses 'u' and 'v' interchangeably.
[History of U and V]
Solution 3:
Something similar happens with the letters i and j—at least in the first volume of Samuel Johnson's Dictionary of the English Language (1756), where, for example, you'll find consecutive entries for jam, jamb, iambick, and jangle, and later for jasmine, jasper, iatroleptick, and javel.
It isn't that Johnson thinks that i and j are identical or indistinguishable. His introduction to the letter i is clear on the relevant distinctions as well as on the combined treatment:
I is in English considered both as a vowel and consonant. I vowel has a long sound, as fine, thine, which is usually marked by an e final ; and a short sound, as fin, thin. ...
J consonant has invariably the same sound with that of g in giant ; as jade.
The second volume of Johnson's Dictionary offers a similar treatment of u and v, with vaward immediately preceding uberty, and udder immediately preceding veal, for example.
Here is Johnson's discussion of u and v:
V, has two powers, expressed in modern English by two characters, V consonant and U vowel. U, the vowel, has two sounds ; one clear, expressed at other rimes by eu, as obtuse ; the other close, and approaching to the Italian u, or English oo, as obtund.
V, the consonant, has a sound in English, uniform. It is never mute.
Solution 4:
As the other answers mention, the b in your example is just a v with ascender because it's the first letter in the word.
BUT, confusing b and v is an easy mistake to make - especially for people whose first language is Spanish, because in Spanish b and v are both pronounced like the English b.
The mixup of b and v also happened in other romance languages and is called betacism.