Question 127079
 x dogs and y pets other than dogs
{{{15x + 5y >= 30}}}
{{{5y >= -15x + 30}}}
{{{y >= -3x + 6}}}
---------------------
{{{x + y <= 10}}}
{{{y <= -x + 10}}}
{{{ graph( 600, 600, -5, 20, -5, 20,-3x + 6, -x + 10 ) }}}
The solutions are between the two lines, including
the lines also, but only in the positive x and y regions
(one cannot care for negative number of pets)
As a check, I can test some points that are in the 
solution zone and one outside
Inside: (8,1), (1,7)
Outside: (1,2)
(8,1)
{{{y >= -3x + 6}}}
{{{y <= -x + 10}}}
------------------
{{{1 >= -3*8 + 6}}}
{{{1 >= -18}}} Ok
-----------------
{{{1 <= -8 + 10}}}
{{{1 <= 2}}}
=======================
(1,7)
{{{7 >= -3*1 + 6}}}
{{{7 >= 3}}}
------------------
{{{7 <= -1 + 10}}}
{{{7 <= 9}}} OK
=======================
(1,2) should not work
{{{2 >= -3*1 + 6}}}
{{{2 >= 3}}} NOT OK
So, this is outside and fails as it should