The motion can be modeled as

where 
x = the position below the equilibrium position
T =  the period of the motion
t = time
The weight returns to its equilibrium position when x = 0. 
This occurs when

That is,

Because the weight returns to the equilibrium position when t =  3 s, therefore
T = 12 s
The motion is

When t = 1 s, the position of the weight from equilibrium is

Answer:
