Since you understand the product rule, you must use a little chain rule on it also. Remember, derivative of inside times derivative of outside.
The second part is just:
Derivative of outside: \(\displaystyle \L\\3(5x-1)^{2}\)
Derivative of inside is just 5
So, you have: \(\displaystyle \L\\3(5x-1)^{2}(5)=15(5x-1)^{2}\)
Now, combine it with the other steps and you have it.