$21-11.$ Negus Enterprises has an inventory coinversion period of $50$ days, an average collection period of $35$ days, and a payables deferral period of $25$ days. Assume that cost of goods sold is $80\%$ of sales.

a$.$ What is the length of the firm's cash conversion cycle?

b$.$ If annual sales are $$4,380,000$ and all sales are on credit, what is the firm's investment in accounts receivable?

c$.$ How many times per year does Negus Enterprises turn over its inventory?