To find the sum invested, we can use the formula for simple interest:

\[
\text{Simple Interest (SI)} = \frac{P \times R \times T}{100}
\]

where:
- \( P \) is the principal amount (the sum invested),
- \( R \) is the rate of interest per annum (5% in this case),
- \( T \) is the time in years (4 years),
- The total amount after 4 years (which is the principal plus interest) is given as \(\#6,000\).

Step-by-Step Calculation:

1. Let the principal amount be \( P \):

\[
\text{SI} = \frac{P \times 5 \times 4}{100} = \frac{20P}{100} = 0.2P
\]

2. The total amount after 4 years is given as:

\[
\text{Total amount} = \text{Principal} + \text{Interest} = P + 0.2P = 1.2P
\]

3. Set up the equation using the total amount:

\[
1.2P = 6000
\]

4. Solve for \( P \):

\[
P = \frac{6000}{1.2} = 5000
\]


The sum invested is \(\#5,000\)

The correct answer is C - \(\#5,000\)