Answer:
The total repair cost for each store is the cost of repairs added to the sales tax. The amount of money saved will be the difference between the two total costs.
Either one at any given time could be equal to zero. So
x + 2 = 0
x = - 2
x - 18 = 0
x = 18
I've enclosed a graph of this so you can see that the answers I've given are the ones expected.
Divide 12 by 72. this equals 6. then multiply. 7x6=47 3x6=18 and 5x6=30 there we go!
I have solved some examples in the picture
If anything is unclear let me know.
:)