6. 9-5z 5+4t -- + --= 5z 4t 3z+2t t+3s

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

Ответ: $$ \frac{36t+25z}{20tz} $$