A cart moves along a straight horizontal track. At time \(t = 0\), the cart has an initial velocity of \(v_0 = 4.0 \text{ m/s}\). The acceleration of the cart as a function of time \(t\) is given by \(a(t) = C t\), where \(C = 3.0 \text{ m/s}^3\). What is the velocity of the cart at time \(t = 2.0 \text{ s}\)?