Acceleration is change in velocity over change in time. Your Δv is +13.9, since you increased speed by 50 km/h which is 13.9 m/s, and your Δt is 10s. 13.9/10 = 1.39 m/s^2, the standard units for acceleration. Make sense?
In order to figure this out you use the equation acceleration = final velocity - initial velocity / time. or a = vf-vi/t. So a = 50 km/h - 0 km/h / 10 seconds. Since 50 - 0 is 50, 50 divided by 10 is 5. So you acceleration is 5 km/h plus the direction you are traveling. So your answer should look like a=5km/h + direction
