To find out how many years it will take for a bank deposit that yields $802.50 in interest annually to accumulate $6.42 \times 10^4 (or $64,200) in total interest, you can use the formula:
\[ \text{Number of years} = \frac{\text{Total interest}}{\text{Annual interest}} \]
Substituting the values, we have:
\[ \text{Number of years} = \frac{6.42 \times 10^4}{802.50} \]
Calculating this gives:
\[ \text{Number of years} = \frac{64200}{802.50} \approx 80 \]
Now, to express 80 in scientific notation:
\[ 80 = 8.0 \times 10^1 \]
Thus, the answer is:
\[ \boxed{8 \times 10^1} \]