A=l√[(w/2)²+h²+w]+w√[(l/2)²+h²]
where
l is base length
w base width
h is height
given that the slant side of our pyramid is 856.1 ft with square base of 145 ft, the height of the pyramid will be found by Pythagorean theorem.
c²=a²+b²
hence:
856.1²=a²+72.5²
a=853.025 ft
The Lateral area is therefore going to be:
A=145√[(145/2)²+856.025²+145]+145√[(145/2)²+856.025²]
A=249,136.0025 ft²