Sorry for posting it so early in the week, but I really thought this problem was interesting :3

Acetic acid has pKa 4.74, so using the Henderson-Hasselbach equation:

4 = 4.74 + log (A-/HA)

A-/HA = 0.18

Therefore, the ratio of acetate to acetic acid in the 0.1M buffer is 0.18, and we can say the concentration of acetate is 0.015 M and the concentration of acetic acid is 0.085 M.

Applying the same equation to the buffer of pH 4.5, we get a ratio of 0.58, and with the buffer of pH 5 we get a ratio of 1.82. If we assume 1 liter of both buffers, and the concentration of the pH 5 buffer to be x, we can write:

(0.015 + 1.82x)/(0.085 + x) = 0.58

For which we can solve and get x ~ 0.0277, meaning the concentration of the pH 5 buffer is 0.0277 M.