Linear functions SAT question

The correct answer is $2$. It’s given that function $f$ is defined by $f(x)=2x+3$. Therefore, the equation representing the graph of $y=f(x)$ in the xy-plane is $y=2x+3$, and the graph is a line. For a linear equation in the form $y=mx+b$, $m$ represents the slope of the line. Since the value of $m$ in the equation $y=2x+3$ is $2$, the slope of the line defined by function $f$ is $2$. It's given that line $j$ is parallel to the line defined by function $f$. The slopes of parallel lines are equal. Therefore, the slope of line $j$ is also $2$.