What is the order of magnitude for 20,000?

If p(a) = 0.70 and p(b) = 0.20, then a and b are independent events if

Annabelle's homework is 75% it took her three hours how long should she estimate it will take her to complete her homework.

The floor of a building consists of 3000 tiles which are rhombus shaped and each of it's diagonals are 45 cm and 30 cm in length. find the total cost of polishing the floor, if the cost per m² is rs. 4.