Let's do the substitution :
Substitute and in the equation :
Simplify by and the equation becomes
This is a first order ODE hence you've to solve the homogeneous equation first : . It'll give a solution . Then, you need to find a particular solution of . As the second member is , you may try . (find by replacing by its expression in ) The solutions of will be given by the sum and then you can use to get the solutions in terms of .