Question 311786
Bob has a very old car that he;d like to replace.
 The old car costs $250 each month for repairs, $120 for each month for gas,
 and $60 each month for insurance.
 A friend is willing to sell him a reliable used car for $7800.
 In addition to the price of the car, this used car will cost $90 each month for
gas and $80 each month for insurance. 
If Bob buys the used car, how long will it take before he begins to save money on car expenses.
 Assign a variable.
:
Let m = the no. of months for him to save money
:
old car expense = new car expense
m(250+120+60) = 7800 + m(90+80}
:
430m = 7800 + 170m
430m - 170m = 7800
260m = 7800
m = {{{7800/260}}}
m = 30 months they are equal and will save money in the 31st month