Answer
$4$
Work Step by Step
RECALL:
$\\\\$The difference quotient of a function $f$ is given by the formula $\dfrac{f(x+h)-f(x)}{h}$ where $h \ne0$.
Use the difference quotient formula above to obtain:
$\dfrac{f(x+h)-f(x)}{h}
\\=\dfrac{4(x+h)+3-(4x+3)}{h}
\\=\dfrac{4x+4h+3-(4x+3)}{h}
\\=\dfrac{4x+4h+3-4x-3}{h}
\\=\dfrac{4h}{h}
\\=4$
