for from 4 to 7, 3
from 7 to 10, 3
so, 3 is the "common difference" then
[tex]\bf n^{th}\textit{ term of an arithmetic sequence}\\\\
a_n=a_1+(n-1)d\qquad
\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term's value}\\
d=\textit{common difference}\\
----------\\
a_1=4\\
d=3\\
n=30
\end{cases}
\\\\\\
a_{30}=4+(30-1)3\impliedby 30^{th}\textit{ term's value}[/tex]
