Formula
F = k*x
Givens
F = 21 N
x = 13
K = ?
Solution
21 = 13 k
21/13 = k
k = 1.615 N / cm
The units are not quiet the ones you should be using. Newtons are found in the mks system.
13 cm [1 m / 100 cm ] = 0.13 m
So an alternate solution is
21 N = k * 0.13 m
k = 21 N / 0.13 m
k = 161.5 Newtons / meter. Answer
