Question 659054
You can think of one boat as standing
still and the other approaching at the
sum of their speeds.
Let {{{ s }}} = the speed of the smaller boat
{{{ s + 4 }}} = the speed of the larger boat
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{{{ 9.8 = ( s + s + 4 )*.7 }}}
{{{ 9.8 = 1.4s  + 2.8 }}}
{{{ 1.4s = 7 }}}
{{{ s = 5 }}}
{{{ s + 4 = 9 }}}
The speed of the smaller boat is 5 mi/hr
The speed of the larger boat is 9 mi/hr