Вариант 1. 18. log_0.8(3) * log_3(1.25)

Заметим, что 0.8 = 4/5, а 1.25 = 5/4 = 1/0.8. log_0.8(3) * log_3(1.25) = log_0.8(3) * log_3(1/0.8) = log_0.8(3) * log_3(0.8^(-1)) = log_0.8(3) * -log_3(0.8) = - log_0.8(3) * log_3(0.8) = -log_0.8(0.8) = -1. Ответ: -1