Answer
(a). $10\ mph$
(b) $30\ mph$, along $\vec v$
(c) $11.3\ mph$ SE (southeast) wind.
Work Step by Step
(a). Given $\vec v=6i+8j$, draw a diagram as shown, the speed of the wind is given by $|\vec v|=\sqrt {6^2+8^2}=10\ mph$
(b) We have $3\vec v=18i+24j$, since $|3\vec v|=30\ mph$, it means a $30\ mph$ wind along the direction of $\vec v$
(c) Given $\vec u=-8i+8j$, we have $|\vec u|=\sqrt {(-8)^2+8^2}=8\sqrt 2\approx11.3\ mph$ and the wind direction is SE (southeast)
