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. You want to set u to be equal to the expression that you have its derivative laying around. So we could set u equal to x to the fourth plus 7. Now what is du going to be equal to? I will do it in magenta. du is just going to be the derivative of x to the fourth plus 7 with respect to x, so 4x to the third plus 0 times dx. I wrote it in differential form right over here, but it's a completely equivalent statement to saying that du, the derivative of u with respect to x, is equal to 4x to the third power.