Hard I need help plz someone help!

  8 gallons

Step-by-step explanation:

Each rectangular face of the monument has an area of ...

  A = bh = (9 ft)(39 ft) = 351 ft^2

The triangular face on top of that rectangle has an area of ...

  A = (1/2)bh = (1/2)(9 ft)(10 ft) = 45 ft^2

So, one side of the monument has an area of ...

  one side = (351 ft^2) +(45 ft^2) = 396 ft^2

The total area of all four identical sides is ...

  surface area = (4)(396 ft^2) = 1584 ft^2

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Each gallon covers 199 ft^2, to the number gallons required is ...

  (1584 ft^2)/(199 ft^2/gal) ≈ 7.96 gal

Since only whole gallons can be purchased, 8 gallons of paint must be bought.