Question 303759
If x is the width of the rectangle and y is the length then x*y=216. We also have y=x+6 so 
x*(x+6)=216
x^2+6x-216=0

so using the quadratic formula to solve for x we get:


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}

{{{x = (-6 +- sqrt( 6^2-4*1*-216 ))/(2*1) }}}

{{{x = (-6 +- sqrt( 900 ))/(2) }}}
{{{x = (-6 +- 30)/(2) }}}
{{{x = (24)/(2) }}}
{{{x = 12 }}}

to find the length of the rectangle we use the expression 

{{{y = x+6 }}}
{{{y = 18 }}}