I'm not sure what to use help me please

Answer:
Mass of the ring is 2.5 kg.
Given:
Moment of inertia of a ring = 0.4 kg.[tex]m^{2}[/tex]
Radius = 40 cm = 0.4 m
To find:
Mass of the ring = ?
Formula used:
I = m [tex]r^{2}[/tex]
Where I = moment of inertia
r = radius of the ring
m = mass of the ring
Solution:
Moment of inertia of a ring is given by,
I = m [tex]r^{2}[/tex]
Where I = moment of inertia
r = radius of the ring
m = mass of the ring
0.4 = m ×0.4×0.4
m = 0.4/(0.4×0.4)
m = 1/0.4
m = 2.5 kg
Mass of the ring is 2.5 kg.