how much of a 30% salt solution must be mixed with 70 gallons of a 12% salt solution to obtain a solution that is 20% of salt?

x(0.3)+(70)(0.12)=(x+70)(0.2)


x(0.3-0.2)=70(0.2-0.12)


x(0.1)=70(0.08)


x=56