You always say that! is that a idiom
metaphor
personification
simile
onomatopoeia
hyperbole?

Hyperbole

Explanation:

A hyperbole is an exaggeration of a rhetorical speech. It may also emphasize strong feelings and create powerful impressions.

substitute y = 2x - 4 to x + 2y = 12:

x + 2(2x - 4) = 12     use distributive property

x + (2)(2x) + () = 12

x + 4x - 8 = 12     add 8 to both sides

5x = 20     divide both sides by 5

x = 4

put the value of x to the first equation:

y = 2(4) - 4

y = 8 - 4

y = 4