Question 713874
{{{ y }}} in the equation is how far from their
destination they are.
Initially, {{{ x = 0 }}} and they are {{{ 500 }}} miles away 
They will have traveled {{{ 112.5 }}} miles when they
are {{{ 500 - 112.5 = 387.5 }}} miles from their
destination, so I can say
{{{ 387.5 = -50x + 500 }}}
{{{ -50x = -500 + 387.5 }}}
{{{ 50x = 112.5 }}}
{{{ x = 2.25 }}}
It will take them 2 hrs and 15 min to travel 112.5 mi