A large greenhouse is built in the shape of a right square pyramid with base lengths of 26 m, and a slant height of 35.4 m. How much glass, to the nearest square metre, is needed for the greenhouse? (Lateral area only)

each face is an isosceles triangle with

base = 26
height = 35.4

I'm sure you know
(a) how to find the area of a triangle
(b) how many faces the pyramid has

plug and chug