what you typed can be interpreted several ways, please use parentheses to clarify
i believe the first question is . personally, i'd combine the fractions first, but multiplying by is a valid option.
note that the whole point of multiplying by the conjugate is to obtain the difference of two squares. hence the numerator will change from the form to the form , and we get
for the second problem, note that you have
which should remind you of the difference of two cubes formula, which should help you know how to proceed.