The telephone bill of a certain establishment is partly fixed and partly varies with the number of calls made. For example, when 540 calls were made, the bill was Rs. 1800, and when 620 calls were made, the bill became Rs. 2040. Using these details:

• Let the fixed charge be Rs. X and the charge per call be Rs. Y.

• From the two given months:
  540Y + X = 1800
  620Y + X = 2040

• Subtracting the first equation from the second gives:
  80Y = 240, so Y = Rs. 3 per call.

• Substitute Y = 3 into the first equation:
  540 × 3 + X = 1800, which gives X = Rs. 180 as the fixed charge.

Thus, the fixed charge is Rs. 180, and the charge per call is Rs. 3.

If the number of calls varies in another month, the bill can be calculated by:
Bill = Fixed charge + (Charge per call × Number of calls) If you provide the number of calls for another month, the specific bill amount can be calculated.