If we take 6/15 and want to make 2/a equivalent to it, we first find out what was done to 6 (the numerator) to make it a 2. The 6 was divided by 3. So we do the same for 15.
15/3=5
The 3rd fraction is 2/5.
You use a similar method for the 4th fraction, b/120.
Now, we find out what was done to 15 (the denominator) to make it a 120.
The 15 was multiplied by 8. So we do the same for 6.
6*8=48
The 4th fraction is 48/120.
For the last fraction 16/c, we use 2/5 as one numerator (16) is a multiple of the other (2).
2 was multiplied by 8 to get to 16, so we do the same for 5.
5*8=40
The last fraction is 16/40.