Exercise 12.2 1. Add 5xy, 6xy and 9xy. 2. Add 2x + 9 and 6x - 5. 3. Add 5x + 13 + 6y and 7x - 11. 4. Subtract m + n - 1 from 5m + 8n - 6 5. Subtract 3y² + 2yz from y² + 5yz + 2². 6. Subtract 21ab6b- 11a from 25ab + 17b- 12a. 7. From the sum of 7x - 2y + 15 and -6y - 18 subtract 5x - 12. 8. What should be subtracted from 5x²-6y² + 7xy + 19 to obtain 3x² - 2y² + 4xy + 31? 32 32 9. Subtract -5x³y²– 2x²y³ - 3y from x + 2x³y² + 4x²y³ + 2yª. 10. How much 15x³ - 21x² is less than 76x³ - 69x² + 9x + 18? FINDING THE VALUE OF AN EXPRESSION​