Final answer:
Lilly's income for last month was $1556.25.
Step-by-step explanation:
To find her income for last month, we need to calculate the commission earned on two different portions of her sales.
First, calculate the commission on the sales up to $4500:
Commission = $4500 * 10% = $450
Next, calculate the commission on the sales over $4500:
Sales over $4500 = $11865 - $4500 = $7375
Commission on sales over $4500 = $7375 * 15% = $1106.25
Finally, add the two commissions together:
Total income = Commission on sales up to $4500 + Commission on sales over $4500
Total income = $450 + $1106.25 = $1556.25