since 3n+2 is even so is 3n

how is 3n even?? and how is 3n+2 even?

if we add subtract an odd number from an even number ,we get an odd number so 3n - 2 = 2n is odd??? i don't get this at all

then it follows that but this is obviously not true, there fore our supposition was wrong, and the proof by contradiction is complete.

i'm so lost i don;t understand what is being said and it is getting really frustrating please help me understand this in English.