3) 810+7 51 51=

3) $$8 \frac{10}{51} + \frac{7}{51} = 8 + \frac{10}{51} + \frac{7}{51} = 8 + \frac{10+7}{51} = 8 + \frac{17}{51} = 8 \frac{17}{51}$$

Ответ: $$8 \frac{17}{51}$$