23. $$\frac{log_9 28}{log_9 7} + log_7 \frac{7}{4}$$

$$\frac{log_9 28}{log_9 7} + log_7 \frac{7}{4} = log_7 28 + log_7 \frac{7}{4} = log_7 (28 \times \frac{7}{4}) = log_7 (7 \times 7) = log_7 7^2 = 2 log_7 7 = 2 \cdot 1 = 2$$

Ответ: $$2$$