I believe that it doesn't make any difference if the pyramid is regular or not.
Total surface area = 2300.
Surface area of the base = 400.
Total surface area of the four sides is 2300 - 400 = 1900.
¾s of the area of each side is below the midline*; therefore ¾·1900 = 1425 is below the midline.
Midline value of each side = 10 ---> area of the top base = 100.
Total surface area = 400 + 1425 + 100 = 1925.
*The reason why three-fourths of the area of the side is below the midline.
Draw any triangle and draw the midline.
Find the midpoint of the base.
Connect line segments from the endpoints of the midline to the base.
You will have created three triangles, each congruent to the triangle above the midline.