Simplex sensitivity — re-checking optimality after a cost change

The final tableau of the simplex method of the LPP $\text{Max}:Z=3x_1+2x_2$ is given below:

$$\begin{array}{c|c|cccc|c} & c_j & 3 & 2 & 0 & 0 & \\ \hline x_1 & 3 & 1 & 0.75 & 0.25 & 0 & 30\\ x_4 & 0 & 0 & 2.25 & -0.25 & 0 & 60\\ \hline z_j-c_j: & & 0 & 0.25 & 0.75 & 0 & 90 \end{array}$$

If the coefficient of $x_1$ in the objective function is changed from 3 to 1, then which of the following statements is/are true? (I) $x_2$ enters as a new basic variable in place of $x_4$. (II) The optimal value decreases by 33.33.