This problem exercises the concept of "similar triangles."
With similar triangles, we can compare the sides using ratios. The equation we can use to find side A is stated below.
Side 1A / Side 1B = Side 2A / Side 2B
The number refers to the triangle, and the letter refers to the side of each triangle. Side A in both triangles must be the base of the triangle, and side B in both triangles can be either of the other sides. The only restriction is that once we pick a side B on triangle 1, we must pick that same side on triangle 2.
