<span>f(n) = f(n-1) + 5 simply means
the next term or f(n), will have a value of
the one before it, or f(n-1), +5
so.. you're looking for the 4th term, that means f(4)
to get 4th term then, that will be the 3rd term plus 5,
whatever the 3rd term is
now... f(1) = -2, simply means, the term 1, or f(1), or first term, is -2
now to find a term value in an arithmetic sequence </span>
![\bf f(n)=f(1)+(n-1)d\\\\ \begin{cases} n=n^{th}\ term\to &4\\ f(1)=\textit{first term}\to &-2\\ d= \begin{array}{llll} \textit{common difference, or amount}\\ \textit{added to get the next term} \end{array}\to &5 \end{cases}\\\\ -----------------------------\\\\ thus \\\\ f(4)=f(1)+(4-1)5](https://tex.z-dn.net/?f=%5Cbf%20f%28n%29%3Df%281%29%2B%28n-1%29d%5C%5C%5C%5C%0A%5Cbegin%7Bcases%7D%0An%3Dn%5E%7Bth%7D%5C%20term%5Cto%20%264%5C%5C%0Af%281%29%3D%5Ctextit%7Bfirst%20term%7D%5Cto%20%26-2%5C%5C%0Ad%3D%0A%5Cbegin%7Barray%7D%7Bllll%7D%0A%5Ctextit%7Bcommon%20difference%2C%20or%20amount%7D%5C%5C%0A%5Ctextit%7Badded%20to%20get%20the%20next%20term%7D%0A%5Cend%7Barray%7D%5Cto%20%265%0A%5Cend%7Bcases%7D%5C%5C%5C%5C%0A-----------------------------%5C%5C%5C%5C%0Athus%0A%5C%5C%5C%5C%0Af%284%29%3Df%281%29%2B%284-1%295)
and I'm sure you know what f(1) is, so, just plug it in, to get f(4), or 4th term