The language "product" means that we must multiply the numbers given to get our answer.
9.0 × 10⁻⁴ m × 8.1 × 10⁴ m = 7.3 × 10¹ m²
The significant figures rule for multiplication is that we must us the amount of significant figures in the number with the least significant figures, in this question this is 2 significant digits from both 9.0 × 10⁻⁴ m and 8.1 × 10⁴ m.
