You can solve by using the pythagorean theorem. If you are given a right triangle, you should have two sides given, and one side missing. The diagonal side is called the hypotnuse, and it's the only side that is important with keeping to the same variable. The pythagorean theorem is: a²+b²=c². C is ALWAYS the hypotnuse. If you are given one leg of the triangle and the hypotnuse, you can plug the leg into EITHER a or b and the hypotnuse in ONLY c. Then you can solve for the other variable. If you are given both legs and asked to find the hypotnuse, you can plug both legs into a and b and then solve for C. Remember that each variable is squared, so if you are solving for C or another side, you need to take the square root to get the variable alone.
This would bring you to $160.00. This is because you initially had $20.00, because of the $13 and $7. Then, your family gave you a total of $140.00, and 140 + 20 = 160.
