"I'll never understand this accounting stuff," Blake Dunn yelled, waving the income statement he had just received from his accountant in the morning mail. "Last month, we sold 1,000 stuffed State University mascots and earned $6,850 in operating income. This month, when we sold 1,500, I thought we'd make $10,275. But this income statement shows an operating income of $12,100! How can I ever make plans if I can't predict my income? I'm going to give Janice one last chance to explain this to me," he declared as he picked up the phone to call Janice Miller, his accountant. "Will you try to explain this operating income thing to me one more time?" Blake asked Janice. "After I saw last month's income statement, I thought each mascot we sold generated $6.85 in net income, now this month, each one generates $8.07! There was no change in the price we paid for each mascot, so I don't understand how this happened. If I had known I was going to have $12,100 in operating income, I would have looked more seriously at adding to our product line." Taking a deep breath, Janice replied, "Sure, Blake. I'd be happy to explain how you made so much more operating income than you were expecting." (a) Assume Janice's role. Explain to Blake why his use of operating income per mascot was in error