ANSWER:
[tex]\begin{gathered} a\text{.} \\ f\mleft(x+h\mright)=3x+3h+4 \\ b\text{.} \\ f\mleft(x+h\mright)-f\mleft(x\mright)=3h \end{gathered}[/tex]STEP-BY-STEP EXPLANATION:
We have the following function:
[tex]f\mleft(x\mright)=3x+4[/tex]Now we calculate the following:
(a) f(x+h)
[tex]\begin{gathered} f(x+h)=3\cdot(x+h)+4 \\ f(x+h)=3x+3h+4 \end{gathered}[/tex](b) f(x+h)-f(x)
[tex]\begin{gathered} f\mleft(x+h\mright)-f\mleft(x\mright)=3\cdot(x+h)+4-(3x+4) \\ f(x+h)-f(x)=3x+3h+4-3x-4 \\ f(x+h)-f(x)=3h \end{gathered}[/tex]