Question 1054203
#2,
w and L dimensions;
{{{system(2w+2L=40+4w,L=2+2w)}}}
-
{{{2+L=20+2w}}}
{{{L=18+2w}}}
{{{2+2w=18+2w}}}----------Unable to isolate w to solve for a value; 
further,
{{{2+2w-2w=18+2w-2w}}}
{{{2=18}}}
{{{cross(2=18)}}}--------No solution!


#3,        
{{{1/6+1/a=1/4&1/2}}}


#1,
See  lessons in profile page.