Let's track the savings for both Natasha and Sal over the months:
Natasha:
- Starting amount: $45
- Monthly addition: $6
- Amount after month \( n \): \( 45 + 6n \)
Sal:
- Starting amount: $55
- Monthly addition: $4
- Amount after month \( n \): \( 55 + 4n \)
We want to find the smallest integer \( n \) for which Natasha's savings exceeds Sal's savings:
\[ 45 + 6n > 55 + 4n \]
Subtract \( 4n \) from both sides:
\[ 45 + 2n > 55 \]
Subtract 45 from both sides:
\[ 2n > 10 \]
Divide by 2:
\[ n > 5 \]
The smallest integer \( n \) that satisfies this is \( n = 6 \).
Therefore, it will take 6 months for Natasha to have more money in her savings account than Sal.
The answer is C. 6.