To determine how many years it will take for a bank deposit that yields $802.50 in interest every year to yield $64,200 (which is \(6.42 \times 10^4\) dollars), we can set up the equation:
\[ \text{Interest per year} \times \text{Number of years} = \text{Total interest} \]
Plugging in the values, we have:
\[ 802.50 \times t = 64200 \]
Where \(t\) is the number of years. To solve for \(t\), we divide both sides by 802.50:
\[ t = \frac{64200}{802.50} \]
Now, calculating this:
\[ t \approx 80 \]
To express this in scientific notation, we rewrite 80:
\[ 80 = 8.0 \times 10^1 \]
Thus, the answer in scientific notation is:
\[ \boxed{8 \times 10^1} \]