The present worth of a certain bill due sometime hence is Rs. 1296 and the true discount is Rs. 72. What is the banker's discount?

$$\eqalign{ & BG = \frac{{{{(TD)}^2}}}{{PW}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{{{72}^2}}}{{1296}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{72 \times 72}}{{1296}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{12 \times 12}}{{36}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{12}}{3} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = {\text{ Rs}}{\text{. }}4 \cr & BG = BD - TD \cr & \Rightarrow 4 = BD - 72 \cr & \Rightarrow BD = 72 + 4 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{.}}\,76 \cr} $$