What is the distance covered by a vehicle moving in a straight line during 20 s if the vehicle changes its speed from 10 m/s to 16 m/s during that time interval?

What is the distance covered by a vehicle moving in a straight line during 20 s if the vehicle changes its speed from 10 m/s to 16 m/s during that time interval? In order to calculate the distance of the boat we first have to identify the suited formula for acceleration in this scenario. 

Hence, a = vf – vi / t. Vi = 10 m/s Vf = 16 m/s T = 20 seconds   

Solution: 
distance = velocity x time
Distance = 16 + 10 m/s / 2 x 20 seconds
Distance = 260 meters

The answer would be c