How do you rationalize the denominator and simplify 7/(sqrtx+sqrty)?

$7 \frac{\sqrt{x} - \sqrt{y}}{x - y}$
Multiply both numerator and denominator by the conjugate of the denominator $\sqrt{x} - \sqrt{y}$ and use
$\left({a}^{2} - {b}^{2}\right) = \setminus \left(a - b\right) \left(a + b\right)$