Answer:
5 * sqrt(3)
Explanation:
First, find the area of the triangle. Do this by determining the height of the triangle. The main triangle is really two right triangles, so do half of it at a time. This causes the base to become one.
According to the Pythagorean Theorem, the height is the square root of 3.
The area of one half of the triangle is sqrt(3)/2, but you need to double that to find the whole triangle's area, so the whole area is sqrt(3).
Now just multiply by 5.
The answer is 5 * sqrt(3), the one you have selected in the image.