Ben earns $750 a month plus 4% commission on all his sales over $900. find the minimum sales that will allow ben to earn at least $2,500 per month.

$750 + s x 4% = $2,500 | - $750

s x 4% = $1,750 | : 4%

s = $43.750

If i think this is what your asking, he should look at the grams or pounds/ounces and compare the to their cost then max can identify which one is proportional and which is not ( i think xd)