1. define they're, there, their2. when do you use a/ an3. define to, too, two

1.They're is the conjunction of they are
There is like location ex. The dog is over there 
Their is associated with a person ex."her taunts had lost their power to touch him"
2. You would use an if there is if the next word begins with a vowel sound and you would use a when the next word begins with a consonant sound
3. How you would use the word to is saying something like I'm giving this to someone how you would use too is like saying this is too much say they add an extra o and two is the number so that is easy to memorize hope I can help!

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

answer: x = 4 and y = 4