ACCORDING TO QUESTION:-
Cucumbers = 6 for $2
Peppers = 12 for $9
Tomatoes = 6 fir $4
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SO NOW
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For 9 cucumbers = as 6 cucumbers is for $2 then 9 will be of $3........1️⃣
For 18 peppers = as 12 peppers are for$9 so 18 will be of $12.........2️⃣
For 21 tomatoes =as 6 tomatoes are for $4 then 21 tomatoes are $14 .......3️⃣
Now add 1️⃣ +2️⃣ + 3️⃣
here $3 +$12 + $14= $29
HOPE IT HELPED YOU.