B is the correct option.
1. Given eqn;
S(t) = 1/2t² - 4t + 8
2.Differentiate the above eqn with respect to t;
d(S(t)) = t - 4
dt
When distance, S, is differentiated it results to velocity.
V = t - 4
at t = 10
V = 10 - 4
V = 6 feet/s
