A lending library has a fixed charge for first three days

A lending library has a fixed charge for first three days and an additional charge for each day thereafter. Rittik paid ₹27 for a book kept for 7 days and Manmohan paid ₹21 for a book kept for 5 days. Find the fixed charges and the charge for each extra day.

Answer

Let fixed charge be ₹x

Let charge for each extra day be ₹y

x + 4y = 27

x + 2y = 21

On solving: x = 15, y = 3

Fixed charge = ₹15

and charge for each extra day = ₹3