Это дроби (2 .3/7 : 4. 4/15 - 5/7 : 1/4) : 1/2 =
(17/7:64/15-5/7*4/1)*2/1= = (17/7*15/64-20/7)*2/1= = (255/448-20/7)*2/1= = ((255-1280)/448)*2/1= = (-1025/448)*2/1= = - 1025/224 = -4 129/224.