Question

how to convert 4.2km/min into km/hr

Answer 1

$1\ hour = 60\ minutes\\\\ 4.2\ km/min= 4.2 \times \frac{km}{min} \times \frac{60\ min}{1\ hour} =4.2 \times 60 \times \frac{km}{hour} =\boxed{252\ km/h}$

Answer 2

4.2 km / min = 252 km / hr
for min to houre multiply it with 60 
because 60 min. = 1 houre
so 
4.2 * 60 = 252 km/ hr