11/21-2 13/5=
решить .

11/21 - 2 13/5 = 11/21 - (5*2+13)/5 = 11/21 - 23/5 =  = (11*5)/(21*5) - (23*21)/(5*21) = 55/105 - 483/105 = (55-403)/105 == (-348/105) = (-3  33/105)