Can someone please help me on this?

f(x) = xcubed - 2xsquared + ax + b, where a and b are constants.

when f(x) is divided by (x-2), the remainder is 1.

when f(x) is divided by (x+1), the remainder is 28.

a) Find the value of a and the value of b.

b) Show that (x-3) is a factor of f(x)

Thanks a lot!