The derivative of x to the fourth is 4x to the third. The derivative of 7 is just 0. So that's a big clue that u-substitution might be the tool of choice here. I'll just write u. I'll write the whole thing. U-substitution could be the tool of choice. So given that, what would you want to set your u equal to? I'll let you think about that because if you can figure out this part, then the rest will just boil down to a fairly straightforward integral.