How do I know if an equation is linear and a function?

ex.
7y - 8 = 20

i dont know if you cant find a way its best to actually add all of them start from 105 tho

step-by-step explanation:

(f - g)(x) = 5x^3 - 3

step-by-step explanation:

rearrange these functions vertically, with like terms in separate columns:

f(x) = 5x^3 - 2

g(x) =         +1

now subtract, column by column:

(f - g)(x) = 5x^3 - 3