For what values of b>0 does 9x=b (mod 12) have solutions within CLOCK12. Solution 9=b (mod 12) ...> 9-b = k*12 where k=constant=0,1,2,3,4,..... b = 9-(k*12) k=0.....> b=9 k=1......> b= -3 therefore 9xb (mod 12) will have only one solution i.e b=9 since b>0 and should be within CLOCK12 Hope this helped.. :).