Kinematics . plz urgent

X1 = (1/2)*g*t^2             (1) 
Then at the end of the 2nd t (total time 2 t), the total distance is 
x1+x2 = (1/2)*g*(2t)^2           (2) 
Multiply both sides of equation #1 by 2. Subtract new #1 from #2. Solve for t.
The answer is Root{(x2-x1)/g}