Hello Jay,
If you let u = x5 + 5 (A)
then du = 5x4 dx (B)
to make it easier to visualize how to substitute, rewrite ∫x4(x5+5)5 dx as ∫(x5+5)5 x4dx
Based on equation (A), you should see that (x5+5)5 can be substituted as u5
Based on equation (B), you should see that x4dx can be substituted as du/5
I'll let you put it all together and finish the question. You got this.