Something like this is good. There is no need to actually simplify the differentiated result, since you are going to substitute the value of x inside the expression anyway.

The question did not ask to find an expression for dy/dx in the prior parts, so there is no need to worry about not simplifying. Even if a question asks for dy/dx, I would rather not simplify an expression if I am not actually very confident of simplifying it.

Did you use quotient rule here? It continues to work, but it’s not going to be a piece of cake to simplify the result. But remember - you are going to substitute x = 4 into the expression regardless.