Equate profits by solving for fee reduction

Steps:

• Original profit: 10 × ($100 -$20) = $800 contribution;$800 - $480 fixed =$320 profit.
• For 20 students: 20 × ($100 - X -$20) = $800 contribution to match profit.
• Simplify: 20 × ($80 - X) =$800.
• Solve: $80 - X =$40 → X = $40.

Why C is correct:

• $40 reduction yields$60 contribution per student × 20 = $1,200 revenue -$880 costs = $320 profit, matching original via equal total contribution.

Why the others are wrong:

• A: $16 reduction →$64 contribution × 20 = $1,280 >$800, higher profit.
• B: $24 reduction →$56 contribution × 20 = 800, higher profit.

Final answer: C