Final answer:
In the quadratic equation 3x² + 4x + 15, the coefficient of x is 4. The coefficient is the constant that multiplies the variable x in the standard form of the equation.
Step-by-step explanation:
The question asks for the coefficient of x in a given quadratic equation. In a quadratic equation of the standard form ax² + bx + c = 0, the coefficient of x is the constant b. Therefore, for the equation 3x² + 4x + 15, the coefficient of x is 4. This is because the equation follows the standard form where a = 3, b = 4, and c = 15.