So the distance covered by Erica = speed x time = 80 x X = 80x

Now the time at which alisha would overtake erica would be one hour less than erica as she started one hour late. Therefore time taken by Alisha = x – 1

So distance covered by alisha = 100(x-1)

Now when alisha overtakes erica, the distance covered by both of them should be equal

Therefore, we get

80x = 100(x-1)

80x = 100x – 100

20x = 100

x = 5

Now substituting the value of x back in the distance covered by erica = 80 x = 80 x 5 = 400 kms

[You can also verify it by substituting th evalue of x in distance covered by Alisha = 100(x-1) = 100 (5-1) = 100 (4) = 400]

Therefore at 400 kms alisha would overtake erica.