When term have the same algebraic factors, they are like terms. Then, we have to add the like terms = t–8tz + (3tz - z) + (z - t) = t–8tz + 3tz–z + z - t = t–t–8tz + 3tz–z + z = t (1 - 1) + tz (- 8 + 3) + z (-1 + 1) = t (0) + tz (- 5) + z (0) = - 5tz