$1.$ of the $$9,000$ of social security benefits received, only $$7,650$ are included in gross $($taxable$)$ income. Why not all of it or none of it$?$ What are the minimum maximum amounts of the $$9,000$ of Social Security benefits received that can be included in the Shackleton$$s gross income?

Due to the Provisional income exceeding the first threshold $(32000$ Joint$),$ and also exceeding the second threshold $(44000$ Joint$).$ Due to being above the second threshold, they must include $85\%$ of the Social Security which is the $7650=9000*85\%.$

If the provisional was within guidelines of only the first threshold then it would have been $50\%$ of the $9000.$

$2.$ Note that on the tax return line $3$b$,$ordinary dividends$$ includes both $$qualified$$ and $$nonqualified$$ dividends. Often when people, even tax accountants, refer to ordinary dividends, they are referring to nonqualified dividends. This is not necessarily right or wrong, but it is something to keep in mind when discussing dividends and when preparing tax returns. Also, reviewing exhibit $16\mathrm{.}1$ may be helpful. You may also want to look at the $$Qualified Dividends and Capital Gains worksheet$$ generated with your tax return.

$2$a$.$ Why are qualified dividends listed separately on the tax return?

Qualified dividends are taxed at the same rate that applies to long term capital gains, while non qualified dividends are taxed at ordinary income rates.