Find the Cardinal number of the set of all solutions to x^2=100

Aswimming pool is a rectangle with semicircles on the end. the rectangle is 12 meters wide and 30 meters long. the diameter and width of the swimming pool are equal. sketch and label an overhead diagram of the swimming pool. find the area of the swimming pool floor.

Tickets to a science exposition cost $5.75 each for studentd and $7.00 for adults. how many students and adults went if the ticket charge was $42.75

We just started the introduction into circles and i have no idea how to do this.