The length of a poster is 2 times its width, if the perimeter is 72 inches what is the area of the poster

What values of c and d make the equation true?

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?

Can someone tell me if this is perpendicular? !