Look to be honest this is what I got hopefully it is right my bad if they aren’t.
Check the picture below
for the DB length, make sure your calculator is in Degree mode, since the angles are in degrees.
You apply the rule to put the exponent in front, and lower it by one. But since this is a nested expression, you apply it twice:
4*(5x^3-4)^3 * 3*5x^2 =
60x^2 (5x^3-4)^3
I don’t know the answer too hope you find some that can help