3x-4a+5a-3x+a=?
3x - 4a + 5a - 3x + a = ?
let's rearrange the numbers so that we have like variables beside each other, we can do that since addition is commutative
3x - 4a + 5a - 3x + a = 3x - 3x - 4a + 5a + a ................now add all the x's and a's together
.............................= 0x + 2a
.............................= 2a