Hi DFSF D
The Lateral Area of Square Pyramid is
Lateral Area = (Perimeter of the base x Slant Height)/2
Above you give the Length of the Base but as stated we don't know if you mean the length of one side of the base is 750, or if the entire length of the base is 750. If 750 is the entire length of the base then it is also the Perimeter of the Base.
We need to know if 750 is the length of one side of your square base or if it is the perimeter of your square base? Need to know so we can help you?