Формула Байеса
Р = (6/15)*0.5/((6/15)*0.5+(9/15)*0.9)=10/37=~0.27
(х-4)÷7/8=5/4×(х-7)
(х-4)×8/7=5/4х-35/4
8/7х-32/7=5/4х-35/4
32х-128=35х-245
32х-35х=-245+128
-3х=-117
х=39