To find out what percent $4 is of $80, you can use the formula:
\[ \text{Percentage} = \left( \frac{\text{Part}}{\text{Whole}} \right) \times 100 \]
Here, the "Part" is $4 and the "Whole" is $80. Plugging in these values, we have:
\[ \text{Percentage} = \left( \frac{4}{80} \right) \times 100 \]
Calculating the fraction:
\[ \frac{4}{80} = 0.05 \]
Now, multiplying by 100 to get the percentage:
\[ 0.05 \times 100 = 5 \]
Thus, $4 is 5% of $80.
The final answer is:
\[ \boxed{5%} \]