Question 1021942
x, side length of the square
b, base of the triangle
h, height of the triangle


{{{system(x^2=(1/2)bh,b=3+x,h=-1+b)}}}


You can solve this system for all three variables, but you are interested in b and h.


Here is a possible start.
{{{b=h+1}}}
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{{{b=x-3}}}
{{{h+1=x-3}}}
{{{x-3=h+1}}}
{{{x=h+1+3}}}
{{{x=h+4}}}
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Substitute this into the area equation:
{{{(h+4)^2=(1/2)bh}}}
But you ALSO have a relation between b and h which you can substitute...
{{{highlight((h+4)^2=(1/2)(h+1)*h)}}}
which is an equation in only one unknown variable, h.   Simplify and solve this for h.