Answer: 52 MPH
Because as you can see at the (Miles) it is 300 above like 4/60,
and 52 is the best choice
explanation :
6 x 52 = 312
312 is the closest to 300
and if you pick the other ones you get:
42 x 6 = 252 "Not Close"
72 x 6 = 432 "Over 300"
32 x 6 = 192 "Not Close"