Answer:
480 inches squared
Explanation:
The formula for the area of a rhombus is pq/2, where p and q are the diagonals. In the picture, half of a diagonal is 10 (which I am assuming 10 does not represent the whole diagonal), so all of the horizontal diagonal is 20.
Applying the Pythagorean Theorem to this, we get 10^2 + x^2 = 26^2. After simplifying, this becomes 100 + x^2 = 676, and therefore x = 24. Multiply this by 2 to get the full vertical diagonal, the area is simply 48*20/2 which is 480 inches squared.