John decided to start rowing around a square lake.  Each side of the lake is 15 miles.  Jake can row at twice the speed he can swim.  It takes him 20 minutes to swim 1 mile.  How long, in hours, does it take to row the lake?
The perimeter of the lake is 4*15=
<gadget id="calculator">4*15</gadget>
<output>60</output>
60 miles.
He swims at a speed of 60/20=
<gadget id="calculator">60/20</gadget>
<output>3</output>
3 mph.
So he rows at a speed of 3*2=
<gadget id="calculator">3*2</gadget>
<output>6</output>
6 mph.
That means it takes him 60/6=
<gadget id="calculator">60/6</gadget>
<output>10</output>
10 hours to row around the lake.

<result>10</result>