"It is mountain"? Oh! "mounted".
You are told the height of the tank but not the radius. Okay, just call that "R". What is the volume of a cylinder with radius R and height 10?
Finding the volume of the water is a little harder. You will need to integrate to find the area of a portion of a circle of radius R (> 7) up to a chord 7 ft above the base of the circle.