Motion — practice question

A skier moves down a slope. The diagram illustrates how his speed changes with time. What is his average acceleration over the $6.0\,\text{s}$?

• A$2.2\,\text{m s}^{-2}$
• B$4.3\,\text{m s}^{-2}$
• C$8.0\,\text{m s}^{-2}$
• D$13.0\,\text{m s}^{-2}$