After jumping out from the plane, a parachutist falls 80 m without friction. When he opens up the parachute, he decelerates at\[2\text{ }m\text{ }{{s}^{-2}}\]. He reaches the ground with a speed of\[4m\text{ }{{s}^{-1}}\]. How long did the parachutist spend his time in the air? (Take\[\text{g=10 m }{{\text{s}}^{\text{-2}}}\])

• A. 4s                                
• B. 16 s                 
• C. 18 s                 
• D.        22 s