Answer:
4 bags will be required.
Explanation:
Patio is in the shape of a parallelogram.
Formula for the area of a parallelogram is,
Area =

= 16.2 × 12
= 194.4 square feet
∵ 50 square feet area is covered by 1 bag of concrete mix.
∴ 1 square feet area will be covered by
bag of concrete mix
∴ 194.4 square feet patio will require the concrete mix =

= 3.888
≈ 4 bags
Therefore, 4 bags of concrete mix will be required by Dave to add a new patio.