the recursive rule

the recursive rule of sequence is f(n)=f(n-1)-6 if the first term is 20 what is the fourth term of the sequance

$\begin{array}{rcll} f(n) &=& f(n-1) - 6 \\\\ f(2) &=& f(1) - 6 \qquad f(1) = 20\\ f(2) &=& 20 - 6 \\ f(2) &=& 14 \\\\ f(3) &=& f(2) - 6 \qquad f(2) = 14\\ f(3) &=& 14 - 6 \\ f(3) &=& 8 \\\\ f(4) &=& f(3) - 6 \qquad f(3) = 8\\ f(4) &=& 8 - 6 \\ \mathbf{f(4)} &\mathbf{=}& \mathbf{2} \end{array}$