1) [(2x+3)x4:5+6]+7-8=92
(2x+3)x4:5+6=93
(2x+3)x4:5=87
(2x+3)x4=435
2x+3=108,75
2x=105,75
x=52,875
2)(780+a):750-318=457
(780+a):750=775
780+a=581250
a=580470
3){[(x-8)x7+6-5]-4}x3-2=10
{[(x-8)x7+1]-4}x3=12
[(x-8)x7+1]-4=4
(x-8)x7+1=8
(x-8)x7=7
x-8=1
x=9