Subtraction is the anwer. 7.8x+7.8y=50*7.8 7.8x+4.3y=50*5.14 ================ 3.5y=50(7.8-5.14) Here's the breakdown 7.8x-7.8x=0 7.8y-4.3y=3.5y 50*7.8-50*5.14=50(7.8-5.14)