Observe that the sequence increases by adding three units. It's an arithmetic sequence.
Let's use the arithmetic sequence formula.
[tex]f(n)_{}=f(1)_{}+(n-1)d[/tex]
Where, f(1) = 7, d = 3. Let's replace these values.
[tex]\begin{gathered} f(n)=7+(n-1)\cdot3 \\ f(n)=7+3n-3 \\ f(n)=3n+4 \end{gathered}[/tex]
Hence, the answer is D.
