How to solve this math problem?

Question

Julie makes $200 bi weekly and spends $50 every paycheck, saving the rest. She currently has $550 in savings. Billy makes $300 bi weekly and only spends $20 per pay check. He does not have a savings. How many months will it take for Billy to surpass Julie's savings?

I remember there was a certain formula when I was taking precalculus, but now I just don't remember at all. Thanks for helping me out!

Answer 1

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x = number of biweekly paychecks

Julie = Billy

550 + (200 - 50)x = (300 - 20)x

550 + 150x = 280x

Subtract 150x from both sides

550 = 130x

Divide both sides by 130

x ≈ 4.23

billy will pass Julie on the 5th paycheck

which is 2.5 months <––––––