Solution:
Consider the following function:
[tex]f(x)=3x+7[/tex]then, the difference quotient of the given function is:
[tex]\frac{f(x+h)-f(x)}{h}=\frac{(3(x+h)+7)-(3x+7)}{h}[/tex]this is equivalent to:
[tex]\frac{(3x+3h+7)-(3x+7)}{h}[/tex]this is equivalent to:
[tex]\frac{3x+3h+7-3x-7}{h}=\frac{(3x-3x)+3h+(7-7)}{h}[/tex]this is equivalent to:
[tex]\frac{3h}{h}=\text{ 3}[/tex]so that, we can conclude that the correct answer is:
[tex]3[/tex]