Ten dollars ????????

Answer

ladies pay 250$ for room rent

waiter got 20$

ladies get back 30$

or

in your way

ladies paid 90x3 = 270$  (Total expense)

less waiter tip = 20$

so room rent  250$

 Rs 10 not gone anywhere it was just an imaginery amount.

Total Cost = Rs. 3 women * Rs 90 each = Rs 270

Waiter's Tip = Rs 20

Hence Room Rent = Rs 270- Rs 20 = Rs 250

$ 270 already includes the dollar kept by clerk. (90*3). Total expenditure 270. Each women has been returned back $ 30. So Total $ 300.