What sum of money will amount to Rs. 520 in 5 years and to Rs. 568 in 7 years at simple interest?

(Principal + Interest) in 5 years → 520
(Principal + Interest) in 7 years → 568
$$\eqalign{ & \therefore {\text{Interest in 2 years = 48}} \cr & \therefore {\text{I = }}\frac{{{\text{48}}}}{2}{\text{ }} \cr & \,\,\,\,\,\,\,\,\,{\text{ = Rs}}{\text{. 24 in one year}} \cr & \therefore {\text{P = 520 - 24}} \times {\text{5}} \cr & \,\,\,\,\,\,\,\,\,\,{\text{ = Rs}}{\text{. 400}} \cr} $$