You said that you knew that differentiates to , and that's the only rule you need to know to differentiate the function you gave.
Because differentiation is a linear operator, you can break the function up into little parts, and differentiate them separately, and then add them back together at the end.
So first of all, find the derivative of , which you know to be , then find the derivative of . Now, you can do that using the same rule because . So the derivative of 2x is simply
So to conclude, the derivative of is , and the derivative of is , therefore, the derivative of is .
Doing it the 'long way', you should have this: