I did this problem already but want to make sure my steps are correct, please show all work/explanations

1) Initially, a lake has 12 pounds of salt in 120 gallons of water. Such a pond has pure water flowing into it at a rate of 6 gallons per minute. The contents of the lake are kept thoroughly mixed, and flow out at a rate of 4 gallons per minute. Set up and solve a differential equation to find the amount of salt y(t) of the mixture at any time t (in minutes).