A lending library has a fixed charge for the first three days and additional charge for each day thereafter.

Solution:

To find:

(1) the fixed charge

(2) The charge for each day

Let the fixed charge be Rs x

And the extra charge per day be Rs y.

According to the given conditions,

$x+4 y=27$

      $x+4 y-27=0$....(1)

      $x+2 y=21$

      $x+2 y-21=0$....(2)

Subtracting equation 1 and 2 we get

$2 y=6$

$y=3$

Substituting the value of y in equation 1 we get

$x+4(3)-27=0$

$x+12-27=0$

$x-15=0$

$x=15$

Hence the fixed charge is $x=$ Rs 15 and the charge of each day $y=$ Rs 3