There is a mistake 9,12,13 is not a right triangle. but 9,12,15 is. IF you use this triangle instead, then the area of the 13,14,15 triangle is the sum of the area of the other two triangles.
Since x is our unknown number, on one side of our equation we will have the "<span>Subtracting two times a number from 10", and on the other will be -3. So,
-3=10-2x</span>
Answer- 6.25 Your welcome.