A boat can cover a distance of 7.2 km downstream and 3.2 km upstream in 2 hours.It can also cover 1.5 km downstream and 0.6 km upstream in 24 minutes. What is the speed of the boat when going downstream (in km/h)?

A

$$4\frac{1}{2}$$

B

6

C

5

D

$$7\frac{1}{2}$$