9000 x 500 = 4,500,000. Think of it as 9 x 5 (=45) with 3 zeros (from the 9000) and 2 more zeros (from the 500) written after it.
81,000,000
40
the area of 500 x 500 is 250 000.
7*9000 = 63000
500 x 6 = 3,000