In a code language, if SPEED is written as 811222223, then how will LINEAR be written in the same language?

Let's look at the opposite positional values (Z=1, Y=2, ..., A=26) for the letters of SPEED:
Opposite of S is H →8

Opposite of P is K →11

Opposite of E is V →22

Opposite of E is V →22

Opposite of D is W →23

Combining them gives: 811222223.
Applying the same opposite alphabetical position values to LINEAR:

Opposite of L is O →15

Opposite of I is R →18

Opposite of N is M →13

Opposite of E is V →22

Opposite of A is Z →26

Opposite of R is I →9

Combining these values sequentially gives: 15181322269.