Relative humidity = \(\frac{\text{mass of water vapour in a given volume of air(m)}}{\text{mass of water vapour needed to saturate same volume of air at same temp(M)}}\) x 100%

R.H = \(\frac{\text{m}}{\text{M}}\)  = \(\frac{0.05}{0.15}\) x 100%

Therefore, relative humidity of the air = 33.33%