To find out how much Mrs. Perez should write the check for, you need to subtract the amount she paid in cash from the total price of the refrigerator.
Total price of the refrigerator: $1368.25
Amount paid in cash: $497.80
Now, perform the subtraction:
\[ 1368.25 - 497.80 = 870.45 \]
Thus, Mrs. Perez should write the check for $870.45.