Question

1+{2×[3+(4+c):5]-6}×7=15

Answer 1

{2x[3+(4+c):5]-6}x7=15-1
2x[3+(4+c):5]-6=14:7
2x[3+(4+c):5]=2+6
[3+(4+c):5]=8:2
(4+c):5=4-3
4+c=1x5
c=5-4
c=1

Answer 2

{2x[3+(4+c):5]-6}x7=15-1=14
2x[3+(4+c):5]-6=14:7=2
2x[3+(4+c):5]=2+6=8
3+(4+c):5=8:2=4
(4+c):5=4-3=1
4+c=1x5=5
c=5-4=1