Astone is falling freely from rest and the total distance covered by it in the last second of its motion equals the distance covered by it in the first 3 seconds of its motion. how long does the stone remain in air?

First we will need the equation for how long which is t=the square root of 2d/g. t is time, 2 times distance then divide gravity to it. BUT before we get into it lets get the equation for distance d=1/2gt^2 then d=1/2(9.8)(3)^2 = d= 44.1 m
now we can solve for the time t= √2d/g then t=√2(44.1)/ and divided by 9.8 which is the gravity. so the final answer is 3 seconds!