In what point in life do i kneed to know algebra?

There are many other examples of real-world uses of algebra, from comparing prices on similar products in a grocery store, to figuring out what time you need

You start learning algebra in high school, so you will need it then. you will also probably need it in college and depending on what career you choose to go into later in life, you may need it then. 
let me know if you have any further questions
:)

The answer would be b

Just divide the x axis (the top) by 2 or multiply the y axis (the bottom) by 2