An electric power plant uses energy from burning coal to generate steam at \(450^{\circ} \mathrm{C}\). The plant is cooled by \(20^{\circ} \mathrm{C}\) water from a nearby river. If burning coal provides \(100 \mathrm{MJ}\) of heat, what is the theoretical minimum amount of heat that must be transferred to the river during the conversion of heat to electric energy?

A. \(100 \mathrm{MJ}\)

B. \(90 \mathrm{MJ}\)

C. \(60 \mathrm{M}\)

D. \(40 \mathrm{MJ}\)