Explanation:

- First Step: Understand that three successive discounts equate to a single composite discount.

- Second Step: Calculate the effective discount of the first two discounts using the formula:

$$(1 - 0.10) \times (1 - 0.04) = 0.90 \times 0.96 = 0.864$$

- Third Step: The equivalent discount after applying the first two discounts is 13.6% (100% - 86.4%).

- Fourth Step: We need another discount (X%) on this remaining amount to bring the total discount to 19%.

- Fifth Step: Set up the equation:

$$0.864 \times (1 - X) = 0.81$$

- Sixth Step: Solve for X:

$$1 - X = \frac{0.81}{0.864} \\

1 - X = 0.9375 \\

X = 1 - 0.9375 = 0.0625 = 6.25\%$$

Thus, the rate of the third discount is Option 3: 6.25%.