Simplify by combining like terms: 3x squared + 7x + 9 + 7x squared + 9x + 8.

1. Group the like terms: the x squared terms, the x terms, and the constants. 2. Combine the x squared terms: 3x squared plus 7x squared equals 10x squared. 3. Combine the x terms: 7x plus 9x equals 16x. 4. Combine the constants: 9 plus 8 equals 17. 5. The result is 10x squared plus 16x plus 17. 6. The option ending in 17x plus 16 swaps the two sums, and 21x squared multiplies the coefficients 3 and 7 instead of adding them. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 1 "Foundations", section 1.2 Use the Language of Algebra_