The total displacement of the object can be calculated by finding the area under its velocity-time graph. We can divide the motion into three segments:

1. Segment 1 (0 to 4 seconds): The object accelerates uniformly from rest (0 m/s) to 20 m/s. This forms a triangle on the velocity-time graph. Displacement $s_1 = \text{Area of triangle} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 4 \text{ s} \times 20 \text{ m/s} = 40 \text{ m}$.
2. Segment 2 (4 to 6 seconds): The object moves at a constant velocity of 20 m/s for 2 seconds. This forms a rectangle on the velocity-time graph. Displacement $s_2 = \text{Area of rectangle} = \text{base} \times \text{height} = 2 \text{ s} \times 20 \text{ m/s} = 40 \text{ m}$.
3. Segment 3 (6 to 8 seconds): The object decelerates uniformly from 20 m/s to rest (0 m/s) in 2 seconds. This forms another triangle on the velocity-time graph. Displacement $s_3 = \text{Area of triangle} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 2 \text{ s} \times 20 \text{ m/s} = 20 \text{ m}$. The total displacement is the sum of the displacements in each segment: Total Displacement = $s_1 + s_2 + s_3 = 40 \text{ m} + 40 \text{ m} + 20 \text{ m} = 100 \text{ m}$.