Equivalent expressions

The question

Which expression is equivalent to 3x + 8 + x?

Which is the same as 3x + 8 + x?

3x + 8 + x≡?

3x + 8 + x=4x + 8

not:12x

x = 3

3x + 8 + x→20

4x + 8→20

x = 1:3x → 33x² → 3

x = 0:3x + 8 + x → 8every x gone

x = 3:3x + 8 + x → 204x + 8 → 20

Equivalent means the two expressions give the same answer whatever x is.
Only the x terms can join: 3x and the bare x are 4 lots of x. The 8 is not an x, so it cannot go in with them and stays where it is.
Adding the 8 in as well would give 12x — but 8 is just 8, not 8x.
Check it by putting a number in — the same number in both. With x = 3: 3x + 8 + x is 20, and 4x + 8 is 20. They match.
You can test any choice this way. Avoid x = 0 or 1 — too many different expressions agree there.

How it works.

01
Equivalent means the two expressions give the same answer whatever x is.
02
Only the x terms can join: 3x and the bare x are 4 lots of x. The 8 is not an x, so it cannot go in with them and stays where it is.
03
Adding the 8 in as well would give 12x — but 8 is just 8, not 8x.
04
Check it by putting a number in — the same number in both. With x = 3: 3x + 8 + x is 20, and 4x + 8 is 20. They match.
05
You can test any choice this way. Avoid x = 0 or 1 — too many different expressions agree there.