Answer: s + 30 ≥ 50; s ≥ 20
Explanation:
let s be the amount you have yet to spend in order to reach $50 or more
you already have $30.
This means you need to spend at least $20 more ($50 - $30 = $20)
S can be greater than or equal to $20 because your total will be 50 or more, therefore qualifying for the discount.