What is the law of cosines and how do I use it to find an angle when I am given side A side C and angle A?

Which fraction below is equivalent to 10/12?

Apool measures 100 meters by 100 meters a toddler inside the pool and trows a ball 60 centimeters from one edge of the pool.how far is the ball from the opposite edge of the pool

Need same math paper but the back now i hope your able to read it cleary i need with hw