1 - For this one I am not too sure as I generally only work with values that require an unknown. This one is an unknown asking for the values to see the fraction equivalent to 3/4 however if I had to guess here it would probably be 9/12 as it asks what is equal to 3/4. 3 goes into 9 3 times and into 12 4 times so it equals 3/4. Note: 9/12 has a numerator less than the denom but so does 6/8 which is the lesser fraction and still equals 3/4.
2 - Well simply put. [tex] \frac{5}{15} = \frac{1}{3} [/tex]
3 - For this one we have to do a bit of work.
Basically just make an equation such as n for numerator and d for denominator.
d = 2n - 4
Now all we have to do is plug in.
2 * 3 - 4 = 2
2 * 6 - 4 = 8
2 * 9 - 4 = 14
2 * 12 - 4 = 20
So now we know our numerator or n equals 12.
The denominator or d equals 20 so we would get the fraction of....
[tex] \frac{12}{20} [/tex]