The distance will be the integral of the velocity vs time. Since we dont have much info we have to assume the velocity increases linearly from 0 to 60 (constant acceleration). Therefore, Velocity will be a function of t, whose slope is 60/7.78, so we take the integral of this line from t=0 to t=7.78 and we arrive at the equation romanom provided. That's where the calculus comes in

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