This is because 5 ( the length of the hypotenuse for the small triangle) times 3 equals 15 (the length of the hypotenuse for the bigger triangle). It's only natural that you would find x times 3 equals 12. x(4) times 3 equals 12
therefore 4 is your answer :) I hope I helped, and gosh I love triangle problems like this xD
Do you have any more? If so you can post them and I can do them for you!
