Grady received $8,680 of Social Security benefits this year. Grady also reported salary and interest income this year. What amount of the benefits must Grady include in his gross income under the following five independent situations? (Leave no answer blank. Enter zero if applicable.) a. Grady files single and reports salary of $13,300 and interest income of $370. Answer is complete but not entirely correct. b. Grady files single and reports salary of $23,320 and interest income of $720