Question 1033582
0.12x + 0.00*2 = 0.07*(x+2)

==> 0.12x = 0.07x + 0.14

==> 0.05x = 0.14  ==> x = {{{highlight(2.8)}}} gallons of 12% acid must be added to pure water to get 7% acid.

I leave the elaboration to other tutors if they wish so.