Pls help on these and thku

What are “like terms”? why can we only add like terms?

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

In the diagram, ab is tangent to c, ab = 4 inches, and ad = 2 inches. find the radius of the circle.