Answer:
Revenues
January = $0
February $4,100 * 50% = $2,050
March $4,100 * 30% = $1,230
April $4,100 * 20% = $820
Expenses
January = $0
February $2,000 * 50% = $1,000
March $2,000 * 30% = $600
April $2,000 * 20% = $400
Operating Income
January = $0
February $2,050 - 1,000 = $1,050
March $1,230 - $600 = $630
April $820 - $400 = $420