3) \frac{5}{18}c+\frac{7}{24}c-\frac{11}{36}c;

3) Упростим выражение:

$$\frac{5}{18}c+\frac{7}{24}c-\frac{11}{36}c=(\frac{5}{18}+\frac{7}{24}-\frac{11}{36})c=(\frac{20}{72}+\frac{21}{72}-\frac{22}{72})c=\frac{19}{72}c$$

Ответ:$$\frac{19}{72}c$$