1).

Suppose that a certain fortunate person has a net worth of $77.0 billion ($7.70 × 10^10).

If her stock has a good year and gains $3.20 billion (3.20 × 10^9) in value,

her new net worth is $8.02 billion ($8.02 × 10^10)

2).

Suppose that this individual now decides to give

one-eighth of a percent (0.125 %) of her new net worth to charity.

$1.00 billion ($1.00 × 10^10) dollars are given to charity.

77.0 billion

+3.2 billion

---------------

80.2 billion

Answer

$80.2 billion <-- new net worth

UPDATE:

80.2 billion * 0.125%

= 80.2 * 0.125/100 (billion)

= 0.10025 billion

= 100.25 million

Round to 3 digits:

= $100 million <-- donated to charity

7.70×10^10+3.20×10^9 = 8.02×10^10

7.70 x 10^10 + 3.20 x 10^9

Need them to be the same power of ten.

7.70 x 10^10 + 0.320 x 10^10

8.020 x 10^10

8.02 x 10^10