Jim creates mixtures for new candies. His boss gives him 20 pounds of 12% milk powder, and 32 pound of 20% milk powder. How many pounds of 12% milk powder jim uses if

Boss wants him make 30 pounds of 18% milk powder for candies.

Please help to answer , and formula also
thanks

amount of 12% powder --- x

amount of 20% powder --- 30-x

.12x + .20(30-x) = .18(30)
times 100
12x + 20(30-x) = 18(30)

solve for x