A rectangle is 6 units wide and x-8 units long. It has the same area as a triangle with a height of 7 units and a base of x-3 units. What is the area of the rectangle?

Rectangle Area ##=lw##
Triangle Area ##=1/2bh##
Set the two areas equal to each other solve for x then substitute x back into the area for the rectangle.
##6xx(x-8)=1/2xx7xx(x-3)##
Simplify …
##6x-48=3.5x-10.5##
##2.5x=37.5##
##x=15##
Area of Rectangle ##=6xx(x-8)=6xx(15-8)=42##
[Note: 42 is also the area of the triangle]
hope that helped