The sum of two numbers are 100 and the difference is 50

Question

My sister got stuck on this problem and I need help.

Answer 1

Since we know that X = 75, create an equation.

x+y=100

75+y=100

-75 -75 (We subtract 75 from both sides.)

y=25

Answer 2

x + y = 100

x - y = 50

2x = 150

x = 75

What is y?