Ask "what if n doubled?" The exponent tells you the multiplier.

Big-O is about growth, not seconds. If the work is proportional to n, doubling n doubles it; if it is proportional to n squared, doubling n multiplies it by 2 squared. Checking every pair among n items takes n(n-1)/2 steps: 10 items give 45 pairs, 100 items give 4,950.

Read it once, then a question tests whether the trick stuck.