Since the triangles are similar, a proportion can be made. 12 = 3 * ? and 20 = ? * ? We know that 3 * 4 = 12, so the proportion must be by 4. Replace 4 into one of the question marks in 20 = ? * ?. 20 = 4 * ? We know that 4 * 5 = 20, so x must equal 5. Your answer is 5.
