Ireally need the answers for these i don't understand this

I tryed my best to figure out what all of the numbers were. if i got any wrong then please tell me and i will put the right answer in the comments.

1) 3/5= 5/x   (cross multiply)
     3x=5(5)
     3x=25
       x= 25/3 -or- 8.33

2) 2/4=x/12   (cross multiply)
 2(12)=4x
     24=4x
       6=x
3) 10/x=5/9   (cross multiply)
   10(9)=5x
       90=5x
       18=x
4) 5/5=x/18   (cross multiply)
 5(18)=18x
     90=18x
       5=x