Please answer the following question by reasoning step-by-step.
A fast-food chain offers free delivery for a minimum purchase of $18. Danny ordered 2 quarter-pounder burgers for $3.20 each, 2 large fries that cost $1.90 each, and 2 milkshakes that cost $2.40 each. How much more worth of food should he order to avail of the free delivery?

3
Two quarter - pounder burgers cost $3.

20 x 2 = $6.

40.

Two large fries cost $1.

90 x 2 = $3.

80.

Two milkshakes cost $2.

40 x 2 = $4.

80.

The total amount spent for the burgers, fries, and shakes is $6.

40 + $3.

80 + $4.

80 = $15.

Therefore, he should order $18 - $15 = $3 worth of additional food to take advantage of the free food delivery.

.

So, the answer is 3