Ahorizontal line on a velocity/time graph shows acceleration.

Zero acceleration

Explanation:

In a velocity-time graph, the gradient of the line describes how the acceleration varies.When the gradient is positive, it means we have a line that is upward sloping thus the accelaration is positive.When we have a negative gradient, it means the line is downward sloping thus the accelaration is negative.When the gradient is zero, there is no slope, thus the accelaration is zero, the case of a horizontal line.

ill do it for 100, also this isnt 80 its 40