L-K
1) Gathering data from the question.
K=n(n+1)
L=m²
2) Let's plug the values in
K=9(9+1)
K=9(10)
K=90
L=(7)²
L=49
3) To find L-K is to subtract those:
L-k
49-90
-41
4.5m questions
5.8m answers