Question: Which of the following is not an expression?
$3x + 4$
$x - 5$
$6x - 3 = 5$
$1 - \frac{x}{4}$
1. The problem asks to identify which of the given options is not an expression.
2. An expression is a combination of numbers, variables, and operations without an equality sign.
3. Let's analyze each option:
- $3x + 4$: This is an expression because it contains variables and constants combined by addition.
- $x - 5$: This is also an expression for the same reason.
- $6x - 3 = 5$: This contains an equality sign $=$, so it is an equation, not an expression.
- $1 - \frac{x}{4}$: This is an expression involving subtraction and division.
4. Therefore, the option that is not an expression is $6x - 3 = 5$.
**Final answer:** $6x - 3 = 5$ is not an expression; it is an equation.