Answer:
$2.50 + $1.20x
$20
Explanation:
Monica needs to buy a gallon of milk ($2.50), but she also wants to buy yogurt which is $1.20 each. However, her total cost has to be under $20, and she doesn't know how much yogurt she can get. So the number of cups of yogurt is unknown, so it is represented by the variable x. Now, the milk and the unknown number of cups of yogurt must be less than or equal to $20.