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
Amount to write the check for = Total cost - Amount paid in cash
Amount to write the check for = $986.23 - $497.80 = $488.43
So, Mrs. Perez should write the check for $488.43.