(a) Find the point $Q$ that is a distance 0.1 from the point $P = (3, 6)$ in the direction of $\mathbf{v} = \left<-2,1\right>$. Give five decimal places in your answer.
$Q =$ ( , )

(b) Use $P$ and $Q$ to approximate the directional derivative of $f(x,y) = \sqrt{x+3y}$ at $P$, in the direction of $\mathbf{v}$.
$f_{v} \approx$

(c) Give the exact value for the directional derivative you estimated in part (b).
$f_{v} =$