Step-by-step explanation:
To find displacement using velocity - time graph, we need to find area under the curve during time period 0 to 20 seconds.
Displacement [ area of Triangle (b=10 units & h=1 units) - area of trapezium (sum of parallel sides=30 units & h=1 unit)
= (1/2 * 10 * 1) - (1/2 * 30 * 1)
= - 10 m