(78-12: 2): (100-16*4)=2*х: (3125-56: 28) (72-(80-416: (3-х): 16))*15+75 !

(78-6):(100-64)=2Х:(3125-2)
72:36=2х:3123
2х:3123=2
2х=2*3123
2х=6246
х=3123

72-(80-416:(3-х):16)=75:15
72-(80-416:(3-х):16)=5
80-416:(3-х):16=72-5
80-416:(3-х):16=67
416:(3-х):16=80-67
416:(3-х):16=13
416:(3-х)=13*16
416:(3-х)=208
3-х=416:208
3-х=2
х=3-2
х=1