An initial value problem, and rate of change problem

Hi, I was having a bit of trouble with the following problems, any advice would be greatly appreciated.

" dy/dx +2y=f(x) where f(x)= {x, 0<=x<3 and 0, x>=3} with the known value y(0)=0 "

and also

" A tank contains 40 gallons of pure water. Brine with 3 lb of salt per gallon flows in at the

rate of 2 gal/min. The thoroughly stirred mixture then flows out at the rate of 3 gal/min.

a. Find the amount of salt in the tank when there are 20 gallons of brine in the tank.

b. When is the amount of salt in the tank greatest? Provide an exact (symbolic) answer

as well as an approximation to one decimal place. Use Calculus techniques. "