it pumps 8 gallons a minute so it is 8x ( 8 gallons times x minutes)
you then need to subtract that amount from 1200
lets say it pumped for 10 minutes, 8 *10 = -80
1200 - 80 =1120
now the answers you have to choose from are kind of tricky because they don't give you the easiet one
so using the numbers above
the formula would be
1120 = -80+1200 =
y =-8x +1200
