Answer:
Step-by-step explanation:
Find the volume of the triangle and then multiply it by the unit cost for the glass:
Supposing the glass is in the shape of an equilateral triangle of side length s.  The height of the triangle is s*sin 60 degrees.  Thus, the area of the triangle is  A = (1/2)(base)(height) = (1/2)(s)(s*sin 60 degrees or approximately
A = (1/2)(s^2)(1/3)√3 square feet.  This simplifies to
A = (1/6)√3s^2 ft^2.
Then the glass cost is (1/6)(√3)s^2($18.75 per ft^2).
