Answer: 70 units
One way to find this answer is to get a very large number line (perhaps from -100 to 100; counting by 1s) and count out the number of spaces from -57 to 13. This method is impractical because it would take a long time.
A shorter method is to subtract the values and make the result positive. So we could say -57 - 13 = -70 which has an absolute value of 70. Or we can say 13 - (-57) = 13 + 57 = 70. Either way, the distance between the values on the number line is 70 units.