ANSWER

Step-by-step explanation
We want to find the period of the spring-mass system when the mass is changed.
The period of a mass-spring system is given by:

where T = period
m = mass
k = spring constant
Substitute the given values for the 3.0 kg mass:

Solve for the spring constant, k:

Now, solve for the period, T, when m = 1.0:

That is its new period.