Question 941014
What they don't say is that the floor of
the dog house is a rectangle- but that's a 
pretty safe assumption.
In a rectangle:
(1) {{{ A = L*W }}}
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given:
{{{ A = 24 }}} ft2
(2) {{{ L = 3W + 6 }}} ft
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Substitute (2) into (1)
(1) {{{ 24 = ( 3W + 6 )*W }}}
(1) {{{ 24 = 3W^2 + 6W }}}
(1) {{{ 3W^2 + 6W - 24 = 0 }}}
Divide both sides by {{{ 3 }}}
(1) {{{ W^2 + 2W  - 8 = 0 }}}
(1) {{{ ( W + 4 )*( W - 2 ) = 0 }}} ( by looking at it )
{{{ W = 2 }}} ( can't use negative result )
and, since
(2) {{{ L = 3W + 6 }}}
(2) {{{ L = 3*2 + 6 }}}
(2) {{{ L = 12 }}}
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The width is 2 ft
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check:
{{{ A = W*L }}}
{{{ 24 = 2*12 }}}
{{{ 24 = 24 }}}
OK