can someone explain it please ?

Answer:
The value of [tex]\theta=63.43^0[/tex]
Explanation:
Range of projectile [tex]\mathrm{R}=\frac{\mathrm{u}^{2} \cdot \sin 2 \theta}{\mathrm{g}}[/tex]
Height of projectile [tex]\mathrm{h}=\frac{\mathrm{u}^{2} \cdot \sin ^{2} \theta}{2 \cdot \mathrm{g}}[/tex]
Here we have
[tex]R=2h\\\\\frac{\mathrm{u}^{2} \cdot \sin 2 \theta}{\mathrm{g}}=2\frac{\mathrm{u}^{2} \cdot \sin ^{2} \theta}{2 \cdot \mathrm{g}}\\\\\sin 2 \theta=\sin ^{2} \theta\\\\2\sin \theta\cos \theta=\sin ^{2} \theta\\\\\tan \theta=2\\\\\theta=63.43^0[/tex]
Range be R and height be h
[tex]\boxed{\sf R=\dfrac{u^2sin2\theta}{g}}[/tex]
[tex]\boxed{\sf h=\dfrac{u^2sin^2\theta}{2g}}[/tex]
ATQ
[tex]\\ \sf\longmapsto R=2h[/tex]
[tex]\\ \sf\longmapsto \dfrac{u^2sin2\theta}{g}=\dfrac{2u^2sin^2\theta}{2g}[/tex]
[tex]\\ \sf\longmapsto sin^2\theta=sin2\theta[/tex]
[tex]\\ \sf\longmapsto sin^2\theta=2sin\theta cos\theta [/tex]
[tex]\\ \sf\longmapsto \dfrac{sin^2\theta}{sin\theta cos\theta=2[/tex]
[tex]\\ \sf\longmapsto \dfrac{sin\theta}{cos\theta}=2[/tex]
[tex]\\ \sf\longmapsto tan\theta=2[/tex]
[tex]\\ \sf\longmapsto \theta=tan^{-1}(2)[/tex]
[tex]\\ \sf\longmapsto \theta=63.4°[/tex]