To find the total cost of the girl's purchases, we need to add the prices of the sweater, blouse, and scarf together.
- Sweater: $21.00
- Blouse: $14.98
- Scarf: $4.97
Now, let's add these amounts:
\[ 21.00 + 14.98 + 4.97 \]
First, we can add the sweater and the blouse:
\[ 21.00 + 14.98 = 35.98 \]
Next, we add the cost of the scarf:
\[ 35.98 + 4.97 = 40.95 \]
Therefore, the total cost of her purchases is $40.95.