To find the combined population of North and South America, we can add the two populations together:
\[ \text{Population of North America} = 5.15 \times 10^8 \] \[ \text{Population of South America} = 3.04 \times 10^8 \]
We will add these two values:
\[ 5.15 \times 10^8 + 3.04 \times 10^8 = (5.15 + 3.04) \times 10^8 = 8.19 \times 10^8 \]
So, the combined population of North and South America is:
\[ \text{Combined Population} = 8.19 \times 10^8 \text{ people} \]
The correct response is:
C. \( 8.19 \times 10^8 \)