The expression is .

First add 

Both have different signs, so subtract the lesser absolute value from greater absolute value.

             (Different signs: Subtract  from )

                           (Since >, the sum has the same sign as ) 

The expression is changed to 

Both have different signs, so subtract the lesser absolute value from greater absolute value.

               (Different signs: Subtract  from )

                           (Since , the sum has the same sign as 27)

The sum is .