To find the domain $D(f)$ of the function given:

$y = \sqrt{3 - x + 5.2 - 81}$

we need to analyze the expression inside the square root because the square root function is only defined for non-negative values. Therefore, we need:

$3 - x + 5.2 - 81 \geq 0$

Simplify the expression:

1. $3 + 5.2 = 8.2$
2. $8.2 - 81 = -72.8$

This gives:

$-x - 72.8 \geq 0$

or

$x \leq -72.8$

Thus, the domain of the function $D(f)$ is:

$(-\infty, -72.8]$

Now, looking at the answer choices, it appears none of the provided options match this exact result. Therefore, the correct response would be:

"Інша відповідь" (Another answer)