Answer:
Since S (displacement) = v * t
you can calculate the area under the graph
S = 1/2 * 3 * 15 - 3 * 13 = 22.5 - 39 = -16.5 m
In the triangular area the object travels at an average speed of 7.5 m/s
for 3 sec = 22.5 m
In the rectangular area the object travels at an average speed of -3 m/s
for 13 sec = -39 m.
So the net distance traveled is 22.5 - 39 = -16.5 m