AYou'll notice from "c)" that the distance the object travelled was 75m, so you get \(V_a_v_e_r_a_g_e = 75m/15s = 5 m/s\).
b) \(a = dV/dT\), so \(a = (0-10)/15\) and then you get \(a = -2/3 m/s ^{2}\).
c) \(S = S_0 + V_0T + 0,5aT^2\) and you get \(S = 10T - (2/6)T^2\) and you plug in \(T = 15s\) and you'll get \(S = 75m\)
