Writing an rk3 algorithm to solve IVP of the form y' = Ay + b(x)

Hi, as a piece of homework i've been given the problem of implementing an rk3 algorithm of the form [x, y] = MyRK3(A,bvector, y0, interval, N)to solve an ivp of the form y' = Ay + b(x) where the function handle bvector, should take the form b = bvector(x) where the input is the location x (which may vary inside the RK step), and the output is the vector b that is needed, together with the matrix A =A to define the system y' = Ay + b(x)

And basically i am really struggling with the function b = bvector(x), and have no idea where to start so could someone please point me in the right direction as to how to go about this?

many thanks, Tristan