Explanation:
$2.00x-($.10x)=3+x
the x would stand for cups and since you already get 3 more cups in a day than before then you would put 3+x_how many cups you sell. the $2.00 is for how much money each up is. and the -$.10 is subtracting 10 cents for each cup you sell.
I dont know if this is correct but this is how I would make my equation