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.