To solve this problem it is necessary to apply the concepts related to Hooke's law.
By definition the force through the theory formulated by Hooke is defined as
[tex]F = k \Delta X[/tex]
Where,
k = Spring constant
[tex]\Delta X =[/tex]Displacement
Part A)
[tex]F = k \Delta X[/tex]
[tex]k=\frac{F}{\Delta X}[/tex]
Therefore
[tex]\Delta X = \frac{F}{k} = 20m[/tex]
At this point our new spring constant would then be given by
[tex]k' = 2K[/tex]
[tex]\Delta X' = \frac{F}{2k} = \frac{20}{2}[/tex]
The expression that indicates how much has been displaced would be
[tex]\Delta X' = 10m[/tex]
Part B) If the length is doubled then the expression for the spring constant is
[tex]K'' = \frac{k}{2}[/tex]
Then the displacement would be
[tex]\Delta X' = 2\Delta X[/tex]
[tex]\Delta X' = 2*60[/tex]
[tex]\Delta X' = 120cm[/tex]