Correct format for [Plural noun] of [physical quantity] [values]
That's a very awkward construction, "of length." You would say, "Two lines, 9 cm and 10 cm long,..." which actually isn't a sentence. There's no verb in there.
As a math teacher, I'd say, "Please draw two lines, one 9 cm long and one 10 cm long." As Barn and Phil noted, "of length" doesn't sound right.