You are lying on a beach, your eyes 20 cm above the

sand. just as the sun sets, fully disappearing over the horizon,

you immediately jump up, your eyes now 150 cm above the

sand, and you can again just see the top of the sun. if you count

the number of seconds (=t) until the sun fully disappears

again, you can estimate the earth’s radius. but for this problem, use the known radius of the earth to calculate the time