SOLUTION:
 

This is a conversion problem.

Initial speed = 100 kmph

Final Speed = 47 kmph

Reduction = 100 - 47 =53 kmph and as 1kmph =0.625 miles(given),

53 kmph = 53 x (625/1000) = 53 x 5/8 = 265/8 = 33.125 mph

= 33mph(approx.) OPTION B