Sam opened a money-market account that pays 5% simple interest. He started the account with $7,000 and made no further deposits. When he closed the account, he had earned $1,400 in interest. How long did he keep his account open?

To find out how long Sam kept his account open, we can use the formula for simple interest:

\[ I = P \times r \times t \]

where:

• \( I \) is the interest earned,
• \( P \) is the principal amount (initial deposit),
• \( r \) is the annual interest rate (in decimal),
• \( t \) is the time (in years).

From the problem, we have:

• \( I = 1400 \)
• \( P = 7000 \)
• \( r = 0.05 \)

We need to find \( t \). Plugging the values into the formula, we get:

\[ 1400 = 7000 \times 0.05 \times t \]

Now simplify:

\[ 1400 = 350 \times t \]

To solve for \( t \), divide both sides by 350:

\[ t = \frac{1400}{350} = 4 \]

Therefore, Sam kept his account open for 4 years.

The correct answer is C. 4 years.