Question

Find a + b, 2a + 3b, |a|, and |a − b|. a = i + 4j − 3k, b = −4i − j + 5k

Answer 1

Please, one problem at a time.  Haven't you started any of these?

What is a+b?       Write out a and b, one over the other, and then combine like terms:

 1i + 4j
-4i -   j
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-3i + 3j (answer to "a+b").

Please try some of the other problem, sharing your work or at least asking questions whose answers might help you get started.