2. Find $\frac{\partial w}{\partial s}$ and $\frac{\partial w}{\partial t}$ using the appropriate Chain Rule. Evaluate each partial derivative at the given values of $s$ and $t$.
(a) $w = x^2 + y^2$, $x = s + t$, $y = s - t$; $s = 1$, $t = 0$
(b) $w = \sin(2x + 3y)$, $x = s + t$, $y = s - t$; $s = 0$, $t = \frac{\pi}{2}$
