Answer:
The height of triangle EFG is 9 units
Step-by-step explanation:
see the attached figure to better understand the problem
step 1
Find the area of a square ABCD
The area of a square is equal to

where
b is the length side of the square
we have

substitute

step 2
Find the height of triangle EFG
The area of triangle EFG is equal to

where
b is the base of triangle
h is the height of triangle
we have

---> area of triangle EFG is the same that the area of square ABCD
substitute the given values in the formula

solve for h

therefore
The height of triangle EFG is 9 units