The law of equi-marginal utility states that

A. $$M{U_x}.{P_x} = M{U_y}.{P_y} = M{U_z}.{P_z}$$

B. $$\frac{{M{U_x}}}{{{P_x}}} = \frac{{M{U_y}}}{{{P_y}}} = \frac{{M{U_z}}}{{{P_z}}} = M{U_m}$$

C. $$\frac{{M{U_x}}}{{{P_y}}} = \frac{{M{U_y}}}{{{P_x}}} = M{U_m}$$

D. $$\frac{{M{U_x}}}{{{P_x}}} < \frac{{M{U_y}}}{{{P_y}}} < \frac{{M{U_z}}}{{{P_z}}}$$

Answer: Option B