What is the constant of variation for y=4x?

What numbers are included in the set of integers? what numbers are not included?

When george started his current job, his employer told him that at the end of the first year, he would receive two vacation days. after each year worked, his number of vacation days will double up to five work weeks (25days) of payed vacation. how many vacation days will he have in 4 years

Consider the sequence below. 3 , 1 , 1/3 , 1/9 , select the explicit function which defines the sequence.