It's a equilateral triangle. The area of the white region is the area of a sector minus the area of a triangle. The sector is 1/6 of the circle, therefore the area of the sector is 1/6 of area of the circle. The formula of an area of the circle:
The area of the sector: The formula of an area of the equilateral triangle:
So we know that 3 rides costs $21. If you then take 21/3 you get 7, you're then going to take 7x5 and you will get 35. Therefore 5 rides on the MoonCoaster cost $35. Hope this helps!