Can someone please help!!!

Me find the measure to side c and the process to solve the problem you appreciate it : )

Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

Astuntman jumping off a 20-m-high building is modeled by the equation h=20-5t^2, where t is the same in seconds. a high-speed camera is ready to film him between 15m and 10m above the ground. for which interval of time should the camera film him?