An algebraic expression uses letters for unknown numbers, e.g. $2x + 1$. The number in front of a letter is the coefficient.
Collect like terms: $3x + 2x = 5x$. Evaluate by substituting a value: when $x = 4$, $2x + 1 = 9$.
Remember
- Only like terms can be added or subtracted.
- In $5x$, the coefficient is 5.