Heart-Felt Ltd. Makes three products. Relevant per unit data for each product is below. Books Pens Pencils Selling price $9 $12 $14 Variable costs and expenses 3 9.50 12 Machine hours to produce 2 1 2 Assuming 1,500 additional machine hours are available, determine which product should be manufactured? Why? Pencils should be manufactured, since it has the highest contribution margin per the scarce resource Pens should be manufactured, since it has the highest contribution margin per the scarce resource Books should be manufactured, since it has the highest contribution margin per the scarce resource Books should be manufactured, since it has the highest contribution margin per unit