Chuck can ride the merry-go-round 5 times longer than Dave who can only ride it for 10 minutes before getting sick.  Erica can stay on the merry-go-round 30% longer than Chuck before getting sick.  How long can Erica stay on the merry-go-round?
Dave can ride the merry-go-round for 10 minutes and Chuck can ride 5 times longer than Dave so he can ride for 10*5 = 
<gadget id="calculator">10*5</gadget>
<output>50</output>
50 minutes.
Erica can stay on 30% longer than Chuck who can ride for 50 minutes so that's an extra .30*50 = 
<gadget id="calculator">30*.01*50</gadget>
<output>15</output>
15 minutes.
Chuck can ride for 50 minutes and Erica can ride an extra 15 minutes for a total of 50+15 = 
<gadget id="calculator">50+15</gadget>
<output>65</output>
65 minutes.

<result>65</result>