The monthly salary of a sales girl in a cosmetic shop is Rs 11,000 and a certain commission is given as per the monthly sales. The sales of a month is Rs 5,00,000 and the total income of the girl in that month is Rs 21,000. (a) What is her commission amount? (b) What is the rate of commission? (c) What would be the income of the girl, if the sales of the month is Rs. 7,77,000?