To find out how much Mrs. Perez should write the check for, we need to subtract the amount she paid in cash from the total cost of the washing machine.
Total cost of the washing machine = $986.23
Amount paid in cash = $497.80
Now we subtract the cash payment from the total cost:
\[ 986.23 - 497.80 = 488.43 \]
Thus, Mrs. Perez should write the check for $488.43.
So the correct response is:
$488.43