Let's denote the number of windows in the house as \( x \).
For Company A, the total cost \( C_A \) is given by:
\[ C_A = 312 + 12x \]
For Company B, the total cost \( C_B \) is given by:
\[ C_B = 36x \]
To find out when Company A's cost is less than Company B's, we need to set up the inequality:
\[ 312 + 12x < 36x \]
Now, let's solve this inequality:
- Subtract \( 12x \) from both sides:
\[ 312 < 36x - 12x \]
- Simplify the right side:
\[ 312 < 24x \]
- Divide both sides by 24:
\[ \frac{312}{24} < x \]
- Calculate \( \frac{312}{24} \):
\[ \frac{312}{24} = 13 \]
Thus, the inequality simplifies to:
\[ x > 13 \]
This means the house must have more than 13 windows for Company A to be less expensive than Company B. Therefore, if the house has at least 14 windows, Company A will be the cheaper option.