The mixture of 2-propanol and Acetophenone is 50% by mass. You have to figure out the mole fractions before coming up with the final partial pressures for each.
Since 2-propanol is 60 g/mol and Acetophenone is 120 g/mol, and they have equal masses in the solution, there will be twice the moles of 2-propanol as Acetophenone. The mole fraction of 2-propanol has to be 2/3 and Acetophenone's mole fraction is 1/3 (both add to 1).
Now just multiply the mole fractions by the pure partial pressures found in the table.
Acetophenone's final partial pressure: 1/3 * 12 torr = 4 torr
2-propanol's final partial pressure: 2/3 * 48 torr = 32 torr. There ya go.
Taking 4/36 and 32/36 should lead to 11% and 89% respectively.
