Let the fixed charge for first 3 days = Rs. x
And additional charge after 3 days = Rs. y
ATQ
x + 4 = 27----------(1)
x + 2 = 21 ----------(2)
Subtract eqn (2) from (1)
2y = 6
y = 3
Substitute value of in (2)
x + 2(3) = 21
x = 21 − 6
x = 15
Fixed charge = Rs. 15
Additional charge per day = Rs. 3