Let u = (1,2), v = (3,1) and T: $\displaystyle R^{2}\rightarrow R$ be a linear transformation such that T(u)= 4 and T(v)= 5. What is T(-3, 4)? (Hint: Write (-3,4) as a linear combination of u and v.)

I don't really know where to start. I know I have to write (-3,4) as a linear combination of u and v, but what do I do from there?