The electricity bill of a certain establishment is partly fixed and partly varies with the number of units of electricity consumed. When in a certain month 540 units are consumed, the bill is ₹1800. Im another month 620 units are consumed and the bill 16 ₹2040. In yet another month 500 units are consumed. Thebill for that month would be ..........

Let constant amount each month = Rs. $$A$$ and for $$x$$ units consumed it is Rs. $$B$$

=> For a month, total bill = $$A+Bx$$

According to ques, => $$A+540B=1800$$ ------------(i)

and $$A+620B=2040$$ ---------(ii)

Subtracting equation (i) from (ii), => $$80B=240$$

=> $$B=3$$

Substituting above value in equation (i), => $$A=1800-1620=180$$

$$\therefore$$ Bill for 500 units consumed = $$180+(500\times3)=180+1500=Rs.$$ $$1680$$

=> Ans - (A)