What would 672831 be rounded to the nearest ten hundred thousand ten thousand hundred thousand

Ateacher has $80 to buy workbooks. each work book cost $3. if she buys as many workbooks as possible, how much money does she have leftover? a) $2 b) $4 c) $6 d) $8

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much