Consider this option:
1. to simplify given expression (a-b)/b:
[tex] \frac{a-b}{b}= \frac{a}{b}-1;[/tex]
2. to rewrite given expression a/4=b/7:
[tex] \frac{a}{b} = \frac{4}{7};[/tex]
3. to substitute a/b into the simplified expression:
[tex] \frac{a}{b} -1= \frac{4}{7} -1=- \frac{3}{7};[/tex]
answer: -3/7
