Two burettes are filled with solutions: one with 0,1OM CH3COOH solution, second with 0,15M CH3COONa. How many milliliters each solution will need to make 20mL of solution, which pH=4.85
Use the Henderson-Hasselbalch equation.
I would set base = millimols base = mLB*0.15.
mmols acid = mLA(0.1M) = (20-mLB)*0.1
Substitute and solve for mLB, then mLA.