A picture is attached...both involve substitution but what I don't understand is for the first one I know u would be e^7x and du would then be e^7x but where does that leave me? How do I decide what becomes u and what remains e^7x in the function?

For the second I know u would be x^3 and du would be 3x^2 so you'd have 1/3 the integral of u times the square root of...SOMETHING. Now would the x^2 inside the sq root just disappear leaving with 42 or what?