To find the length of the miniature couch for the dollhouse, we first need to convert Janie's couch length from feet to inches, and then apply the scale.
Janie's couch is 7 1/2 feet long. We'll convert this to inches:
7 1/2 feet = 7.5 feet
Now, converting feet to inches (since there are 12 inches in a foot):
\[ 7.5 \text{ feet} \times 12 \text{ inches/foot} = 90 \text{ inches} \]
Next, we apply the scale of 1 inch : 2 feet. This means that each 1 inch in the model represents 2 feet in real life. To find the length of the miniature couch, we can divide the total length in inches by the number of feet represented by each inch in the scale.
\[ \text{Length of miniature couch} = \frac{90 \text{ inches}}{2 \text{ feet/inch}} = 45 \text{ inches} \]
Therefore, the length of the miniature couch for the dollhouse is 45 inches.