Assume that the composition of federal outlays and receipts shown in the figure remained the same in 2019. In the figure, the categories "Defense and homeland security" and "Non-defense discretionary" are discretionary outlays and all other categories are mandatory outlays. Also assume that the total spending was $\$ 5.3$ trillion. Complete parts through (c). Federal Spending Social Security $24 \%$ Medicare $17 \%$ Interest on debt $7 \%$ Medicaid, government pensions and other mandatory spending $24 \%$ Defense and homeland security $16 \%$ Non-defense discretionary $12 \%$ a. About how much was spent (in dollars) on Social Security and Medicare combined in 2019? $\$ \square$ trillion (Type an integer or a dtsimal.)

Step 1 ：Given that the total federal spending in 2019 was $5.3 trillion.

Step 2 ：The percentage of the total spending that was allocated to Social Security was 24% and to Medicare was 17%.

Step 3 ：To find the total amount spent on Social Security and Medicare combined, we need to add the percentages of these two categories and then multiply the sum by the total spending.

Step 4 ：The formula for this calculation is: \( (total spending) \times ((percentage of Social Security / 100) + (percentage of Medicare / 100)) \)

Step 5 ：Substituting the given values into the formula, we get: \( 5.3 \times ((24 / 100) + (17 / 100)) \)

Step 6 ：Calculating the above expression, we find that the total amount spent on Social Security and Medicare in 2019 was approximately $2.173 trillion.

Step 7 ：So, the final answer is \(\boxed{2.173}\) trillion.