Answer
$155\space N/m$
Work Step by Step
Here we use the equation $ W=\frac{1}{2}Kx^{2}$, Where W-work done by the cord, K- spring constant, x- stretched distance of the cord.
$W=\frac{1}{2}Kx^{2}$
Let's plug known values into this equation.
$15.4\space kJ=\frac{1}{2}K(26.3\space m-12.2\space m)^{2}$
$2\times 15.4\times1000\space J= 198.8\space m^{2}\space K$
$155\space N/m=K$
Spring constant = 155 N/m
