If we just see with vertices (0,8) , (8, 0) and (0, 0) then we can ans for any similer question.
Total no of points = 6 + 5 + 4 + ....... + 1.
Similarly, for general case, with vertices (0, n), (n, 0), and (0, 0 ).
Total no of points = (n-2) + (n-3) + (n-4) + .................. + 1.
= $\frac{(n-1)(n-2)}$/2.
So ans for this question = $\frac{39*40}{2}$
= 780.
Ans- A.