Question

-21+3z/7 / 4z-28/49

Answer 1

Since you are not too generous with parentheses, which are required for all numerators and denominators having more than one term, I assume the question is:

(-21+3z/7) / (4z-28/49)
Multiply both numerator and denominator by 7 and simplifying gives:
(3z-147)/(28z-4)
which can be further factored to give
(3/4)(z-21)/(7z-1)