Question 961457
You can think of this as one of them
riding at the sum of their speeds, and
the other one standing still
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Let {{{ s }}} = Bianca's speed in mi/hr
{{{ s + 4 }}} = Haley's speed in mi/hr
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{{{ 84 = ( s + s + 4 )*4 }}}
{{{ 84 = 8s + 16 }}}
{{{ 8s = 68 }}}
{{{ s = 8.5 }}}
{{{ s + 4 = 12.5 }}}
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Bianca's speed is 8.5 mi/hr
Haley's speed is 12.5 mi/hr