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