Due today by midnight

you are standing at the top of a cliff that has a stairstep configuration. there is a vertical drop of 7 m at your feet, then a horizontal shelf of 5 m, then another drop of 3 m to the bottom of the canyon, which has a horizontal floor. you kick a 0.55 kg rock, giving it an initial horizontal velocity that barely clears the shelf below. what initial horizontal velocity v will be required to barely clear the edge of the shelf below you? the acceleration of gravity is 2 answer in units of m/s.