Write the recursive formula for 31, 22, 13, 4, -5, -14.... Select one: O a. t(1)=31, t(k)=t(k-1)+9 O b. t(1)=31, t(k)=t(k-1)-9 O c. t(1)=30, t(k)=t(k-1)-9 O d. t(1)=30, t(k)=t(k-1)-8