I will do 1-4 since there are a lot of questions and let me know if that helps you do the rest and I will help from there if that's okay :)
what we have to do is multiply the first equation by a x/x so that that fraction can be equivalent to the second one.. ( we will find the missing number) :)
Let's get started
1. 3/7= 36/?
The top is multiplied by 12 since 3×12=36
so multiply the bottom by 12 .. 7×12=84
84 is the missing number
2. 2/5=16/?
The top number is multiplied by 8 since 2×8=16
So multiply the bottom by 8 .. 5×8=40
40 is the missing number
3. 5/9=30/?
The top number is multiplied by 6 since 5×6=30
so multiply the bottom number by 6 .. 9×6= 54
54 is the missing number
4. 2/3= 12/?
The top number is multiplied by 6 since 2×6=12
So multiply the bottom by 6 .. 3×6=18
18 is the missing number
* this works the same if you top number is missing figure out what the bottom number is multiplied by and do the same to the top one..