Question

Using 0.1M phosphate buffer, pH 7.2, prepare 25ml each of the buffer solutions with the following concentrations at pH 7.2:
1. 0.005M
2. 0.05M
3. 0.010M

Answer 1

I'm not sure what your problem is. This appears to be just a dilution since the pH of the initial solution is the same as the final; therefore, you aren't being asked to change the ratio of base to acid.
So for C dilute by 10; i.e., dilute 2.5 mL to 25
For B dilute the 0.1 to 0.5; i.e., 12.5 mL of the 0.1 to 25 mL total.
For A dilute B by 10.