i paid 150 to have cable installed and now pay 40 per month

i paid $150 to have cable installed and now pay $40 per month for service. my brother paid $50 to have cable installed and pays $60 a month for service. how many months until we have both paid the same amount for service i think the formula is something like this: 150 + 40m = 50 + 60m

Solution

Your formula is perfect, On the left side is your total cost and on the right side is your brothers total cost. For some value of m they are equal. Solve for m and you will have your answer in months.