Do you only change the limits of integration when substituting? I get confused and don't know when to change the limits of integration.
Now, in order to find this, you must first solve the intergrand. So one way to solve this question is to use the technique of substitution.
So I'm going to let . I have introduced a new variable in place of . In the orginal function, the limit was x from 2 to 4 but now my intergral is in terms of , which MAY OR MAY NOT go from 2 to 4. Thus to find out what it does go to, you plug in into the equation to find out what goes to when goes to 2. And you do the same for the other limit, 4. In the end, you should find the new limits of u to be from 17 to 37.
You then easily find the answer to be since . You can also after solving the integral, re-substitute then solve again in terms of x from 2 to 4. Same answer!
Hope this helps!