On river, Q is the mid-point between two points P and R on the same bank ofthe river. A boat can go from P to Q and back in 12 hours, and from P to R in 16 hours 40 min. How long would it take to go from R to P ?

A

$$ 3 \frac{1}{3} hr $$.

B

$$ 5 hr $$.

C

$$ 6 \frac{2}{3} hr $$.

D

$$ 7 \frac{1}{3} hr $$.