Final answer:
Jill must sell at least 80 more boxes of cookies but no more than 280 more boxes to be eligible for the silver level prize.
Step-by-step explanation:
To determine how many more boxes of cookies Jill must sell to be eligible for the silver level prize, we need to find the range of values that satisfies the compound inequality.
Let x represent the number of additional boxes Jill must sell.
The amount Jill has already sold is $600.
Each box of cookies sells for $5, so the amount she has already sold can be represented as 5 * 600.
Based on the given conditions, the compound inequality is:
1000 ≤ (600 + 5x) ≤ 2000
To solve the compound inequality, we subtract 600 from each term:
400 ≤ 5x ≤ 1400
Next, we divide each term by 5:
80 ≤ x ≤ 280
Therefore, Jill must sell at least 80 more boxes of cookies but no more than 280 more boxes to be eligible for the silver level prize.