Question: what $5$ billion times $1$ trillion?
1. **State the problem:** We need to find the product of $5$ billion and $1$ trillion.
2. **Write the numbers in standard form:**
- $5$ billion = $5 \times 10^{9}$
- $1$ trillion = $1 \times 10^{12}$
3. **Multiply the numbers:**
$$
5 \times 10^{9} \times 1 \times 10^{12} = 5 \times 10^{9+12} = 5 \times 10^{21}
$$
4. **Interpret the result:**
The product is $5$ followed by $21$ zeros, which is $5$ sextillion.
**Final answer:** $5 \times 10^{21}$