5\6(12c+a)+2\3(3c-2a)
=10c+5/6a+2c-8/3a=12c+5/6a-16/6a=12c-11/6a
неправильно
5/6*12c + 5/6*a+2/3*3c-2/3*2a = 10c+5/6a+2c-4/3a = 12c + 5/6a-8/6a = 12c-3/6a=12c-1/2a