Question 1131381
Let {{{ x }}} = number that ordered chicken dinner
{{{ 6 - x }}} = number that ordered steak dinner
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{{{ 14x + 17*( 6 - x ) = 99 }}}
{{{ 14x + 102 - 17x = 99 }}}
{{{ 3x = 3 }}}
{{{ x = 1 }}}
and
{{{ 6 - x = 5 }}}
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1 ordered chicken dinner 
5 ordered steak dinner
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check:
{{{ 14*1 + 17*5 = 99 }}}
{{{ 14 + 85 = 99 }}}
{{{ 99 = 99 }}}
OK