Final answer:
Lily should solve the inequality 6s + 159 ≥ 420 to determine the minimum number of spoon sets to buy. After solving, she should buy at least 44 sets to have enough spoons for the restaurant.
Step-by-step explanation:
Lily needs to ensure the restaurant has at least 420 spoons and there are currently 159 spoons. Since each set contains 6 spoons, we can set up an inequality to find out the minimum number of sets (s) she should buy.
The inequality would be:
6s + 159 ≥ 420
To solve for s, subtract 159 from both sides:
6s ≥ 261
Next, divide both sides by 6:
s ≥ 43.5
Since Lily can't buy half a set, she needs to round up. Therefore, Lily should buy at least 44 sets of spoons to have enough for the restaurant.