To me, do the math using compatible number, means to estimate 7233 can round to 8000 and 84 can round to 80 now, this makes it easy, you can do it mentally, which is 100
In more detailed, 7233 can round to 7225 and 84 can round to 85 then, (not so obvious, but however) 85 times 85 equal 7225
so the compatible number of 7233 divided by 84, is 7225 and 85