Add 4a + 2b, 3a - 3b + c and -2a + 4b + 2c

The correct answer is 5a + 3b + 3c

(4a + 2b) + (3a - 3b + c) + (-2a + 4b + 2c)
= 4a + 2b + 3a - 3b + c + -2a + 4b + 2c
= 4a + 3a - 2a + 2b - 3b + 4b + c + 2c
= 5a + 3b + 3c