You are choosing between two plans at a discount warehouse. Plan A offers an annual membership of $50 and you pay 10% of the manufacturer's recommended list price. Plan B offers an annual membership fee of $30 and you pay 30% of the manufacturer's list price. a. Express the total yearly amount paid to the warehouse under plan A, f, as a function of the dollars of merchandise purchased during the year, x. f(x) = (Use integers or decimals for any numbers in the expression.)