The answer is 25 13/20 square feet.
In order to complete this operation, it is first best to change your mixed numbers into improper fractions.
7 1/8 = 57/8
7 1/5 = 36/5
Now that we have these, we can put them into the triangle formula.
A = 1/2bh
A = (1/2)(57/8)(36/5)
A = 1026/40
You can then simplify this fraction by dividing the top and bottom by a factor of 2.
A = 513/20
Then, because we know 20 goes into 500, 25 times, we can pull that out and be left with a remainder of 13/20.
A = 25 13/20