I need help asap! math problem

Which expression is not a polynomial?

Tatiana reads 40 pages of her book every night for x number of nights. write an expression that shows the number of pages she has read

Long division setup showing an incomplete calculation. 12 is in the divisor, 6839 is in the dividend, and 5 hundreds and 6 tens is written in the quotient. 6000 is subtracted from 6839 to give 839. an unknown value represented by a box is being subtracted from 839. what number should be placed in the box to complete the division calculation?