The expression is .

               (Substitute x = 10, y = – 4 and z = – 15 in original expression)

Additive inverse of  – 4 is 4. To subtract 4, add – 4.

                   (Add: )

Additive inverse of – 15 is 15. To subtract – 15, add 15.

                               (Add: )

The simplified expression is 21.