Question 964996
You could assign variables to everything.

u, one dimension of the canvas
v, other dimension of the canvas
A, total area of frame plus canvas
w, the uniform width of the border


You should draw a picture and label everything because this usually helps.


{{{highlight_green(A=(u+2w)(v+2w))}}}, main equation purely in symbolic form.  The unknown variable is w.


{{{uv+2vw+2uw+4w^2=A}}}
{{{4w^2+(2v+2u)w+uv-A=0}}}
{{{4w^2+(2u+2v)w+uv-A=0}}}
{{{highlight_green(4w^2+(2u+2v)w+(uv-A)=0)}}}.


You could continue in symbolic form to solve for w using general solution formula for a quadratic equation, but maybe more comfortable to substitute the given values NOW, and then use the general formula solution.
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u=22
v=24
A=728