106As the COM of the two particles will travel along the path of the projectile, So, when the two particles reach the ground, u can get the position of the heavier particle
i.e. TAking the pt. of projection as origin,
m1*(R/2) + m2*x = (m1 + m2)R
So x = 7R/6
u can find R and put..
So, x=1120 m ..
ur ans is correct [1]