how to write equations

Question

Mr.Malone is putting  money in two savings accounts.  Account A started with $200 and Account B started with $300.  He deposits $15 in Account A and $10 in Account B each month.  In how many months will the accounts have the same balance? What will that balance be?

Answer 1

a=200+15$/month

b=300$+10$/month

assume dont get interest

200+15m=300+10m

15m -10m=300-200

5m=100

m=20

b:300*10*20=300+200=500$