15) (15+x+y+b)/(4ab) + 7b/(4ab) =

\(\frac{15+x+y+b}{4ab}+\frac{7b}{4ab}=\frac{15+x+y+b+7b}{4ab}=\frac{15+x+y+8b}{4ab}\).

Ответ: \(\frac{15+x+y+8b}{4ab}\)