Need a Formula for this problem

[haveonEuropeanswerex]

A right square pyramid has a surface area of 65.5m² and a base length of 3.5 m. Determine the height of the pyramid

 

[Harry_the_cat]

Draw a diagram. Call the height of the pyramid h. Find the slant height of the triangular faces in terms of h.
The surface area is just the sum of all the faces.
See what you can do from there.