#### Answer

$$8.2 \times 10^{-16} + 4.3 \times 10^{-16}=1.25 \times 10^{-15}$$

#### Work Step by Step

$$8.2 \times 10^{-16} + 4.3 \times 10^{-16}$$
Since both expressions have the same value of exponents in 10, we can just proceed by adding the numerical values.
Thus,
$$8.2 \times 10^{-16} + 4.3 \times 10^{-16}$$ $$(8.2+4.3) \times 10^{-16}$$ $$= 12.5 \times 10^{-16}$$
Since numerical factors in scientific notation must be between 1 and 10, $12.5 \times 10^{-16}$ can be rewritten as:
$$ 1.25 \times 10^{-15}$$