Answer :
[tex](a)\quad a_{n+1}=a_n-6\\\\(b)\quad a_1=20,\ d=2-8=-6\implies a_n=20+(-6)(n-1)\\\\{}\qquad a_n=-6n+26\\\\(c)\quad a_{30}=-6\cdot30+26 = -154[/tex]
[tex](a)\quad a_{n+1}=a_n-6\\\\(b)\quad a_1=20,\ d=2-8=-6\implies a_n=20+(-6)(n-1)\\\\{}\qquad a_n=-6n+26\\\\(c)\quad a_{30}=-6\cdot30+26 = -154[/tex]