Add:

(i) 3mn, -5mn, 8mn -4mn

(ii) t - 8tz, 3tz – z, z - t

(iii) -7mn + 5, 12mn + 2, 9mn – 8, -2mn -3

(iv) a + b -3, b - a + 3, a - b + 3

(v) 14x + 10y - 12xy – 13, 18 - 7x - 10y + 8xy,4xy

(vi) 5m - 7n, 3n - 4m + 2, 2m - 3mn -5

(vii) 4x^{2}y, -3xy^{2}, -5xy^{2}, 5x^{2}y

(viii) 3p^{2}q^{2} - 4pq + 5, -10p^{2}q^{2}, 15 + 9pq + 7p^{2}q^{2}

(ix) ab - 4a, 4b – ab, 4a - 4b

(x) x^{2} - y^{2} – 1, y^{2} - 1 - x^{2}, 1 - x^{2} - y^{2}