There are 60 minutes in 1 hour, therefore, if the car has a speed of 60 kilometers per hour, that simply means, 60 kilometers per 60 minutes.
now, if the car covers 60 kilometers in 60 minutes, that means in 1 minute, it covers 1 kilometer.
now, if we want to cover every kilometer, not in 1 minute, but half-minute faster than that, that means 1 - 1/2, or 1/2 minute, so, what speed is needed to cover 1 kilometer in just half-minute then?
well, you just need to increase your kilometer per minute from 1 minute, to 1/2, that is , 1 kilometer per 0.5 minutes.
if you can cover 1 kilometer in 0.5 minutes, how many can you cover in 60 minutes or 1 hour? in 1 minute you can cover 2 kilometers at that speed, in 60 minutes then, you can cover 120 kilometers, twice as many.
