The user provided an image containing handwritten mathematical expressions. Please extract and format them according to the schema.

Математические выражения:

• \[ \log_3 78 = ? \]
• \[ 12.4 \log_9 13 \]
• \[ \log_5 25^2 \]
• \[ 13.7 \log_7 18 \]
• \[ 14 \log_5 25^2 \]
• \[ 16. \log_3 39 \]
• \[ 17. \log_5 5 + \log_3 7 \]
• \[ 18. \log_9 7^6 - \log_7 7 \]
• \[ 19. \log_5 7 - \log_8 79 \]
• \[ 20. \log_3 3 + \log_9 27 \]