So, I'm doing a math debate/ A dog debate if you wanna call it that

And my math teacher isn't doing a good job explaining it

How am I supposed to write an expression,

(x -2)/ 7
2 human years= 20
3 human years= 28
4 human years= 35

(I'm doing a saint Bernard btw)

(60 -2)/ 7 = 8.2…. 8 is human years]

What else am I supposed to do???

not sure what you are trying to do. It appears that you have a formula for

human = (dog-2)/7
or maybe
dog = 7*human + 2