Use the substitution method to solve the system of equations choose the correct ordered pairs

Use the distance formula to determine the distance that point q is from r on the hypotenusebased on a 2-3 ratio. i need asap !

Match each expression with its simplified form.

Element x decays radioactively with a half life of 8 minutes. if there are 450 grams of element x, how long, to the nearest tenth of a minute, would it take the element to decay to 37 grams?