The graph illustrates how velocity changes with time $t$ for an object travelling in a straight line. When $t = 0$, the object's displacement is zero. What is the displacement of the object at $t = 20\,\text{s}$?
- A$-3\,\text{m}$
- B$21\,\text{m}$
- C$24\,\text{m}$
- D$27\,\text{m}$