15/16(51/3x-4/15y)-7/23(34/21y)

15/16(51/3x-4/15y)-7/23(34/21y) = 15/16*51/3x- 15/16*4/15y-34/69y=

255/16x- 1/4y -34/69y= 255/16x- 69/276y -136/276y=

255/16x- 205/276y =15.15/16х-205/276y