Simplify the expression 7x squared plus 8x plus x squared plus 4x by combining like terms.

1. Identify the like terms: 7x squared and x squared are like terms, and 8x and 4x are like terms. 2. A term written as x squared alone has an implied coefficient of 1, so 7x squared plus x squared equals 8x squared. 3. Add the coefficients of the x-terms: 8x plus 4x equals 12x. 4. Combine both results: 8x squared plus 12x. 5. Dropping the implied coefficient of 1 on the plain x squared term gives the wrong sum, 7x squared plus 12x, instead of 8x squared plus 12x. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 2 "The Language of Algebra", section 2.2 Evaluate, Simplify, and Translate Expressions_