Resposta :
[tex]\Large\boxed{\begin{array}{l}\tt dados\begin{cases}\sf a_n=62\\\sf r=6\\\sf a_1=20\\\sf n=?\end{array}\\\sf a_n=a_1+(n-1)\cdot r\implies n=\dfrac{a_n-a_1}{r}+1\\\\\sf n=\dfrac{62-20}{6}+1\\\\\sf n=\dfrac{42}{6}+1\\\\\sf n=7+1\\\sf n=8\blue{\checkmark}\end{array}}[/tex]