Question 877404
w and L.
2w+2L=140 simplifies to w+L=70.

L=3w.   Length L is larger than width.


Question asks, what is L-w?
Try looking at w+L=70 and L=3w to make substitutions for L-w.
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w=70-L.
L-w=L-(70-L)=L-70+L=2L-70, but the question's answer should be a VALUE.


Solve for L and w, and then finding their difference will or can be a value.
Take the system:  3w-L=0 and w+L=70.  Add left members and right members will eliminate L to show {{{4w=70}}};
{{{w=2*35/(2*2)}}}
{{{w=35/2}}}.
{{{L=3w}}} as found at the beginning of the question.
{{{L=3(35/2)}}}
{{{L=105/2}}}
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{{{highlight(w=35/2)}}} and {{{highlight(L=105/2)}}}.
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The question, what is {{{highlight_green(L-w)}}}?
{{{105/2-35/2=70/2=highlight(35)}}}.