Science Homework Help

There are 2 questions that I have gotten stumped on, I have a big assessment tomorrow and need assistance on the practice.

the first question is, a 6.4kg box moving along the ground at 2.5m/s, is slowed by friction until it comes to a rest. find the coefficient of kinetic friction, if the object moves 1.6.

And the last one is, An object is thrown at a speed of 10m/s toward the ground, from a rooftop. the impact speed with the ground is 15m/s. what is the rooftops height above the ground?