Let the angular speed of disc be ω.

Using conservation of mechanical energy
mg2R=21Idiscω2+21Iparticleω2
Where, I is moment of inertia.
⇒mg2R=2ω2[2m2+mR2]
⇒mg2R=2ω2(23mR2)
⇒43ω2=R2g
⇒ω2=3R8g
Thus, angular speed is ω=3R80rads−1
Given ω=43Rx
Comparing both, 163Rx=3R80
Therefore, the value of x=5.