Calculate osmotic pressure using π=VnRT where n is total moles of solute particles.
Moles of solute A: nA=60 g/mol0.3 g=0.005 mol
Moles of solute B: nB=180 g/mol0.9 g=0.005 mol
Total moles: ntotal=0.005+0.005=0.01 mol
Volume of solution: 100 mL = 0.1 L
Temperature: 27°C = 300 K
Osmotic pressure: π=0.10.01×0.082×300=0.10.246=2.46 atm