The area of a triangular block is 64 square inches. if the base of the triangle is twice the height, how long are the base and height of the triangle?

X=long of the base
y=long of ht height.

Area (triangle)=(b*h)/2

we suggest this system equations:
xy/2=64
x=2y
we solve this system by substitution method:
(2y)y/2=64
y²=64
y=⁺₋√64
Then, we have two solutions:
y₁=-8; invalid solution
y₂=8;    ⇒x=2y=2*8=16:

solution: 
base=16 in
height=8 in