If these two shapes are similar, what is the measure of the missing length h?

Answer:
56 miles.
Step-by-step explanation:
As the triangles are similar corresponding sides are in the same proportion.
h / 68 = 42/51
51h = 42*68
h = (42*68)/51
h = 42 * 4 / 3
h = 14*4
h = 56.