#### Answer

15 inches.

#### Work Step by Step

The scale of the blueprint is $1 inch = 6 feet$.
The length of the house is $90 feet$.
The width of the house is $30 feet$.
We are asked to calculate the length of the house on the blueprint.
The unnecessary piece of information is the house's width since we don't need it to calculate the length on the blueprint.
The length of the house on the blueprint is:
$90 \div 6 =15$ (inches)