Geometry HELP
posted by Ariel .
The lateral surface area of a regular pyramid is 160 cm2 and the perimeter of the base is 40 cm. What is the slant height?

I forgot to put the possible answers,
a.) 4cm
b.) 8cm
c.) 10cm 
See repost:
http://www.jiskha.com/display.cgi?id=1275672571 
thanks :)