arithmetic sequence formula:
[tex]a_n=a_1+(n-1)d[/tex]where:
• an: nth term
,• a1: first term
,• n: term position
,• d: common difference
In this case, the common difference is:
12 - 5 = 19 - 12 = 26 - 19 = 7
and the first term is 5. Then for n = 20:
[tex]\begin{gathered} a_{20}=5+(20-1)7_{}_{} \\ a_{20}=138 \end{gathered}[/tex]