Answer:
8
Explanation:
Isabella's budget line is :
320 = (40 × Quantity of lemons) + (20 × quantity of tangerines)
If she buys all lemons she would buy zero quantities of tangerines
320 = (40 × Quantity of lemons) + 0
Quanitity of lemons = 320 / 40 = 8
I hope my answer helps you