Explanation:

To find the value of S in the equation 15% of 20% of S equals 126, you need to follow these steps:

- Calculate 20% of S:

- 20% is equal to 0.2, so 0.2 times S is how you find 20% of S.

- Calculate 15% of that result:

- 15% is equal to 0.15, so 0.15 times (0.2 times S) is what you need to calculate next.

- Set that equal to 126:

- \(0.15 \times (0.2 \times S) = 126\) simplifies to \(0.03 \times S = 126\).

- Solve for S:

- To find S, divide 126 by 0.03, which results in S = 4200.

- Options Analysis:

- Option 1: 4200

- Option 2: 4500

- Option 3: 4800

- Option 4: 3900

- The correct answer is Option 1: 4200

, as 4200 is the correct choice to satisfy the given condition.