Question

What are the following values in piecewise form:

A) 21x-3

B) 4-3x

Answer 1

Your title says "absolute value", but your expression does not contain that operator.
Is B) y = |4 - 3x| ?

If so, then y = 4-3x or y = 3x - 4
The graph looks like this:
www.wolframalpha.com/input/?i=y+%3D+%7C4+-+3x%7C