3. \(\frac{9-5z}{5z}+\frac{5+4t}{4t}=\)

Общий знаменатель — \(20zt\):

\(\frac{9-5z}{5z}+\frac{5+4t}{4t}=\frac{4t(9-5z)+5z(5+4t)}{20zt}=\frac{36t-20zt+25z+20zt}{20zt}=\frac{36t+25z}{20zt}.\)

Ответ: \(\frac{36t+25z}{20zt}\).