Please Help (Math)

I'm assuming that the slant height   = 10 ft

If so.......we have 4 congruent triangles....each with a base of 10   and a height of 10

Ther total area  = 4 (1/2) base * height  =   4  (1/2) (10) ( 10)  =  200 ft^2  = lateral surface area