Answer and Explanation:
a. The computation of the selling price is given below:
= $9 ÷ (1 - 0.25)
= $12 per unit
b. The number of units that should be sold in the case when the operating income is increased by $7,500
= ($12,000 + $7,500) ÷ ($12 - $9)
= 6,500 units
Hence, the same should be considered and relevant