here's whatcha got
Her I will use the chain rule and the distributive law and make use of the fact that the derivative of a sum is the sum of the derivatives
Now since 50(80) is constant Its derivative is 0 and I finish up with the power rule
Does that help?
I think that you were focused on things that you shouldn't have been. Remember, they want you to find the derivative, so don't focus on tedious multiplications, rather look for ways to get rid of those nasty little constants.