Erin, a sales representative, earns 220 per week plus commission on sales. Erin earns 1% commission on all sales up to 10,000 in a week. If her sales are over 10,000, she earns 3% commission on all additional sales over 10,000. (a) Calculate Erin's commission in a week when she has sales of 8,660. (b) Calculate Erin's total earnings in a week when she has sales of 12,500. (c) Calculate Erin's total sales in a week when she earns commission of 142. (2 marks) (5 marks) (6 marks) (Total 13 marks)