If the triangles are similar, the base should be 24 inches. The legs on the first triangle are 12 inches. To get 36 inches (the other triangle), we multiply 12 by 3. 12 x 3 = 36. Because you did that to the legs, you must also do it to the base. 8 x 3 = 24. Therefore, the base of the second triangle is 24 inches.