As i was solving it again , i realize that i use a wrong formula( i put 8 instead of 64) .

The first attempt to solve this i didn't use the k (spring constant) and i found a result N=0.89

The second time , i did this mistake , and now that i solve it again (as you can see in the picture above ) with the correct formula , i find that N=0.89

I am thinking that it make sense not giving me the formula of spring constant , as i can solve it without it .

BUT

my problem is how is possible N=0.89?? let's assume that N=1 , only one coil ? :/ :/