Question 577193
Let {{{ x }}} = number of tables that seat 4 
Let {{{ y }}} = number of tables that seat 10
given:
{{{ 4x + 10y = 280
{{{  x + y <= 52 }}}
Here's the graph
{{{ graph( 400, 400, -10, 60, -10, 60, -(2/5)*x + 28, -x + 52) }}} 
The possible solutions lie on the line {{{ 4x + 10y = 280 }}}
in the region which is under the line {{{ x + y = 52 }}}
but restricted to (+) values of {{{x}}}