a, $\frac{7}{25y}$ +$\frac{1}{25}$
=$\frac{8}{25}$
b, $\frac{-1}{8}$+$\frac{-5}{8}$
=$\frac{-6}{8}$
=$\frac{-3}{4}$
c, $\frac{3}{5}$+$\frac{-7}{4}$
=$\frac{12}{20}$ +$\frac{-35}{20}$
=$\frac{-23}{20}$
d, $\frac{6}{13}$+$\frac{-14}{39}$
=$\frac{18}{39}$+$\frac{-14}{39}$
=$\frac{4}{39}$
Chúc bạn học tốt!