Problem: The Difference between 2 numbers is 15. If twice the larger number is added to 3 times the smaller, the result is 90. Find the 2 numbers.

If I understood it correctly this would cause the formulas to be...

x - y = 15

2x + 3y = 90.

I need to find the answer for x and y by using BOTH the addition method and substitution method. I keep thinking I have it until I go back and check my answer, then I keep finding out I'm completely wrong. I assume this problem is actually quite easy, but it's frustrating me. Any help would be appreciated.

I need to show my work also. I really want to understand the steps involved so I can see what I'm doing wrong. Thank you.