The formula for the area of a triangle is:
[tex]\frac{Bh}{2} [/tex]
where B is the base of the triangle and h is the height
It appears that the height of the triangle is 5 units (not quite 4.5) and the base is 10 units.
Multiply these to get 50, and divide by 2 to get 25.
The area of the triangle should be 25 u²
Hope this helps! :)