Final answer:
The domain of the linear expression 4x - 9 is all real numbers, as there are no restrictions on x.
Step-by-step explanation:
The expression given, 4x+6-15, simplifies to 4x - 9 which is a linear equation, not a quadratic equation. The domain of a linear equation is all real numbers because there are no restrictions on the value of x for which the expression is defined. In contrast, when dealing with quadratic equations of the form ax² + bx + c = 0, one would use the quadratic formula to find the roots of the equation, which are the values of x where the equation equals 0. However, that is not necessary in this case since we're dealing with a linear equation.