Answer:
416 N\m
Explanation:
Weight of board
[tex]W=ma\\\Rightarrow W=104\ N[/tex]
Length the spring can stretch = Total height of room - (unstrained length of spring + Length of Board)
[tex]2.41-(0.3+1.86)\\\Rightarrow 2.41-2.16=0.25\ m[/tex]
From Hooke's law
[tex]W=kx\\\Rightarrow k=\frac{W}{x}\\\Rightarrow k=\frac{104}{0.25}\\\Rightarrow k=416\ N\m[/tex]
The spring constant is 416 N/m