In this question, you are given 3 separate vegetables without single price. If you want to solve it step by step, it will be easier to count each vegetable price before hand. The price would be:
Cucumber: 2$/6 pieces= $0.33 /piece
Pepper: $9/12 pieces= $0.75/piece
Tomatoes: 4$/6 pieces= $0.66/piece
Then the total cost for the chef shopping item would be: 9 * $0.33 + 18 * $0.75 + 21* $0.66= $3 + $13.5+ $14= $30.5