Answer:
8.083 rad/s ≈ 1.286 Hz
Step-by-step explanation:
The spring constant k is ...
k = Mg/l = (0.25 kg)(9.8 m/s^2)/(0.15 m) = 16 1/3 N/m
The oscillation frequency is ...
ω = √(k/M)
ω = √((49/3 N/m)/(0.25 kg)) ≈ 8.083 rad/s ≈ 1.286 Hz
_____
Additional comment
Since the mass is involved in both the numerator and denominator of ω, it cancels, and we have ...
ω = √(g/l) . . . . . where l is the length the mass pulls the spring from rest.
For this, we don't even need to know the spring constant or the mass.