Problem 1:

	exponent for e = u = 5x, du = 5 dx, "fix" the 5

Problem 2:

	u = x², du = 2x dx, "fix" the 2

Problem 3:

	This is a fraction, but the numerator is not the derivative of the denominator. It is not a log. It is also not a single power of e.
Rewrite the integrand as two fractions and simplify using exponent rules.

Problem 4:

	Rewrite the integrand first.