4. (a) In the expansion of (2x - 3y) , find the coefficient of my' (after combining like terms). (b) In the expansion of (x - 2y + 3z), how many terms are there before combining like terms. (c) In the expansion of (x - 2y + 3z)', find the coefficient of way 2 (after combining like terms). (d) In the expansion of (x - 2y + 3z), how many terms are there after combining like terms