From the sum of 14a + 9b – 8c and 12b + 13c – 15a subtract the sum of 8a – 17b + 4c and 11a – 16b + 17c.

Solution : 

= [(14a + 9b – 8c) + (12b + 13c – 15a)] – [(8a – 17b + 4c) + (11a – 16b + 17c)]
= [(14a + 15a) + (b + 12b) + (8c + 13c)] – [(8a + 11a) + (- 17b – 16b) + 94c + 17c)]
= [- a + 21b + 5c] – [19a – 33b + 21c]
= (- a – 19a) + (12b + 33b) + (5c + 21c)
= – 2a + 45b – 16c