72% as a decimal is 0.72.
72% as a fraction is 72/100 = 18/25.
The factor of mn+5m-3n-15 is 6m-4n-15.
She has to buy both binders and notebooks. So, you have to take into account that she has to have both. The closest you can get to $20 while still getting notebooks, is to buy 4 binders. 4 times 4 equals 16. So, she can get 4 binders and 2 notebooks, because then, 2 times 2 equals 4 and 16 plus 4 equals 20.
Formula is:
Number of reams per case x number of cases
11 x 12 = 132 reams
X=7 (let me know if you would like to know how I got the answer)
