To find out how many years it will take to yield \(6.42 \times 10^4\) dollars in interest, we can use the formula:
\[ \text{Total Interest} = \text{Interest per year} \times \text{Number of years} \]
In this case, the total interest is \(6.42 \times 10^4\) dollars and the interest per year is \(802.50\) dollars. Let \(x\) be the number of years. Then we can set up the equation:
\[ 6.42 \times 10^4 = 802.50 \times x \]
To find \(x\), we can rearrange the equation:
\[ x = \frac{6.42 \times 10^4}{802.50} \]
Now we can calculate \(x\):
\[ x \approx \frac{6.42 \times 10^4}{802.50} \approx \frac{64200}{802.50} \approx 80 \]
Next, we can express \(80\) in scientific notation:
\[ 80 = 8.0 \times 10^1 \]
So the number of years it will take to yield \(6.42 \times 10^4\) dollars in interest is:
\[ \boxed{8 \times 10^1} \]