To determine how long it will take Stacy to paint the entire bedroom, we first find her painting rate.
Stacy paints \( \frac{3}{4} \) of the bedroom in 3 hours. Therefore, her painting rate is:
\[ \text{Rate} = \frac{\text{Area painted}}{\text{Time}} = \frac{3/4 \text{ of the room}}{3 \text{ hours}} = \frac{3}{4} \times \frac{1}{3} = \frac{1}{4} \text{ of the room per hour} \]
Now, to find out how long it takes to paint the entire room, we use the formula:
\[ \text{Time} = \frac{\text{Total Area}}{\text{Rate}} = \frac{1 \text{ room}}{\frac{1}{4} \text{ room/hour}} = 4 \text{ hours} \]
So, the answer is 4 hours (B).