The total pressure is the sum of the partial pressures: Ptotal = PA + P_B.

Step 2: Calculate the partial pressure of gas B.
The total pressure is the sum of the partial pressures: $P_{total} = P_A + P_B$.

$$P_B = P_{total} - P_A = 1.5 \text{ atm} - 1 \text{ atm} = 0.5 \text{ atm}$$

Step 3: Set up the ratio of pressures and masses to molecular weights.
Since pressure is proportional to moles ($P \propto n$) and moles are mass divided by molar mass ($n = \frac{m}{M}$), we have $P \propto \frac{m}{M}$.
Therefore, we can write:

$$$$