Verified answer

 с-12=0

 с=0+12

с=12

х:108=1

х=1*108

х=108

b*15=0

b=0*15

b=0

с-12=0                         х:108=1                              b*15=0

с=12+0                        х=108*1                              b=15:0

с=12                             х=108                                  b=0

12-12=0                      108:108=1                          0*15=0

0=0                               1=1                                       0=0