Question 1111988
Let {{{ t }}} = time in hrs the Stewart family 
used their sprinkler
{{{ 45- t }}} = time in hrs the James family
used their sprinkler
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{{{ 35t + 30*( 45 - t ) = 1500 }}}
{{{ 35t + 1350 - 30t = 1500 }}}
{{{ 5t = 1500 - 1350 }}}
{{{ 5t = 150 }}}
{{{ t = 30 }}}
and
{{{ 45 - t = 15 }}}
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Stewart family: 30 hrs
James family: 15 hrs