Acceleration equals velocity/time. We have time, 6 seconds; but need to find velocity. Using kinematic equations we know velocity equals distance/time. Our distance is 60m and our time is 6s. Giving us a velocity of 60m/6s = 10m/s. Now we input our velocity and our time values into our acceleration equation.
a = v/t. 10m/s / 6s = 60m/s.