Let there are 3 vectors a, b and c where

a = 2i - j + 2k

b = i + 2j - k

c = 5i - 5j - 4k

Now, a + b + c = (2i - j + 2k) + (i + 2j - k) + (5i - 5j - 4k) 

=> a + b + c = i(2 + 1 + 5) + j(-1 + 2 - 5) + k(2 - 1 - 4)

=> a + b + c = 8i - 4j - 3k

In this way, we solve vector tripple sum.