To find 3a + 2b, we first need to find the coordinates of 3a and 2b:

3a = 3(2;1;-5) = (6;3;-15)
2b = 2(0;0;0) = (0;0;0)

Now, we can add these two vectors together to find 3a + 2b:

(6;3;-15) + (0;0;0) = (6;3;-15)

Therefore, 3a + 2b = (6;3;-15)

Next, to find a - 3b, we need to find the coordinates of a and 3b:

a = (2;1;-5)
3b = 3(0;0;0) = (0;0;0)

Now, we can subtract these two vectors to find a - 3b:

(2;1;-5) - (0;0;0) = (2;1;-5)

Therefore, a - 3b = (2;1;-5)