Question 888312
I call this a " head start " problem. The cruise
ship has a {{{ 2 }}} hr head start. 
Let {{{ d[1] }}} = the cruse ship's head start 
in miles.
Let {{{ s }}} = the cruise ship's speed in miles / hr
(1) {{{ d[1] = 2s }}}
This is the head start
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After 2 hrs, the speedboat has traveled
{{{ d[2] = 25*2 }}}
{{{ d[2] = 50 }}} mi
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The vessels are {{{ 90 }}} mi apart after {{{ 2 }}} hrs
The cruise ship has traveled {{{ 2s }}} again in the {{{ 2 }}} hrs 
since the speedboat left
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{{{ 2s + 2s + 50 = 90 }}}
{{{ 4s = 90 - 50 }}}
{{{ 4s = 40 }}}
{{{ s = 10 }}}
The cruise ship's speed is 10 mi/hr
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This makes sense because in {{{ 4 }}} hrs the cruise ship 
traveled {{{ 90 - 50 = 40 }}} mi
{{{ 40/4 = 10 }}} mi/hr
Hope this helps