If you let y = x\^2 + 4, can you calculate dy/dx?
Whether you use u or y or orange as the symbol, it doesn't change what needs to happen.
If orange = x\^2, then d(orange)/dx = 2x
If zztop = x\^2, then d(zztop)/dx = 2x
there is nothing magical about the symbol that changes the mathematical operation.