From the projectile motion we know that the height attained by a projectile is given by :
H=v2sin2α2g
where v = speed
α = angle
Now both A and B acquire same height, hence
Va2sin2452g=Vb2sin2θ2g
sin2θ=Va2Vb2sin245
sinθ=12
θ=30o
A projectile thrown with an initial speed u and angle of projection 15∘ to the horizontal has a range R. If the same projectile is thrown at an angle of 45∘ to the horizontal with speed 2u, its range will be