Solve the following differential equation :

x' = hx + b

if you know that if $\displaystyle x(t_0) = x_0 $

Actually I'm only allowed to use the method of separating the values.

I found the solution but with another way which I'm in fact not supposed to know...

Maybe somebody knows the asked method for this... or at least how I could transform it in something like:

x' = f(x) * g(t)