80 meters.

Remember that:

If you double the speed, the braking distance becomes four times longer.

If you triple the speed, the braking distance becomes nine times longer.

If you quadruple the speed, the braking distance becomes sixteen times longer. If you quadruple the speed, the braking distance becomes sixteen times longer.

You can also calculate it using the formula for the change in braking distance: You can also calculate it using the formula for the change in braking distance:

In this case, you have been given that the braking distance before the increase in speed was 5 meters, and that the speed was increased by 4 times (from 20 km/h to 80 km/h). In this case, you have been given that the braking distance before the increase in speed was 5 meters, and that the speed was increased by 4 times (from 20 km/h to 80 km/h).

Therefore, the braking distance will increase by the square of 4 (which equals 4x4, which in turn equals 16). Therefore, the braking distance will increase by the square of 4 (which equals 4x4, which in turn equals 16).

The braking distance at 80 km/h will then be 5 meters x 16 which equals 80 meters. The braking distance at 80 km/h will then be 5 meters x 16 which equals 80 meters.