What is your end goal? I'd bet you're supposed to calculate the volume fo the building.
If the base is in the form of an equilateral triangle 180 m on each side, then the perpendicular distance from any vertex of the triangle to the opposite side is found using the formula h = (180 m) sin (60 deg), or 180sqrt(3)/2, or 90sqrt(3).
The area of the base is A = bh/2, which here is A = [(180 m)(90sqrt(3))], or
28059 square meters. Then the VOLUME is (28059 m^2)(25 m) = 701475 cubic meters.