To find out how much Carl earned on Thursday, you can multiply the number of wreaths he made by the amount he earns per wreath.
Carl makes 6 wreaths and earns $35.40 for each wreath.
So, the calculation is:
\[ 6 \text{ wreaths} \times 35.40 \text{ dollars/wreath} = 212.40 \text{ dollars} \]
Now, we need to round $212.40 to the nearest dollar.
Since the decimal part is .40, which is less than .50, we round down.
Thus, the estimated amount Carl earned, rounded to the nearest dollar, is:
\[ \boxed{212} \]