can anyone explain (briefly if you want!) why/how:

For Gaussian elimination: At the kth step, we have:

n - k divisions (multipliers)

(n - k)^2 subtractions and multiplications (matrix update)

(n - k) subtractions and multiplications (updating vector b)

how do you get n - k or (n - k)^2

i know you must count the operations, but how?? it looks random

thanks!