b ) 2 / 3 : ( - 7 / 5 ) = 2 / 3 x ( - 5 / 7 ) = - 10 / 21
c ) - 12 / 7 : ( - 3 / 4 ) = - 12 / 7 x ( - 4 / 3 ) = + 48 / 21 = 2 intregi si 6 / 21
