A store bought 120 mugs for $4.00 each and it priced them to yield a mark-up of 50% based on selling price. After Christmas it had forty left over so it priced the remainder to give a mark-up of 50% based on cost. Assuming all sold at this markdown, find:

(a) the regular selling price,

(b) the after Christmas price,

(c) the effective mark-up rate based on sales.