Question 171384
Let w=width of the deck
Area of the pool and deck is:
(10+2w)(5+2w)=50+30w+4w^2 and we are told that this equals 126m^2, so:
4w^2+30w+50=126  subtract 126 from each side
4w^2+30w-76=0 divide each term by 2
2w^2+15w-38=0---------------quadratic in standard form;  solve using quadratic formula:

{{{w = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{w = (-15 +- sqrt( 225+304))/(4) }}} 
{{{w = (-15 +- (23))/(4) }}} 

Neglect negative value for w; widths in this case are positive, so:
{{{w=8/4=2 m}}}-------------------width of deck

CK
(10+4)(5+4)=126
14*9=126
126=126

Hope this helps---ptaylor