Use the Pythagorean Theorem, where the leg lengths are a and b, and the hypotenuse length is c.
[tex] a^2 + b^2 = c^2 [/tex]
[tex] a^2 + (30~in.)^2 = (34~in.)^2 [/tex]
[tex] a^2 + 900~in.^2 = 1156~in.^2 [/tex]
[tex] a^2 = 256~in.^2 [/tex]
[tex] a = 16~in. [/tex]
Answer: 16 in.