Verified answer

1) 25 = 18х                   2) х : 4,5 = 2,1 : 0,63

х = 25:18                       0,63х = 4,5 * 2,1

х = 25/18                       0,63х = 9,45

х = 1 7/18                      х = 9,45 : 0,63

                                       х = 15  

25 : 40 = 18х : 25

40 * 18х = 25 * 25

720х = 625

х = 625: 720

х = 625/720

х = 125/144