To find out how much change Britney should receive, first, we need to calculate the total cost of the shirt and the hat.
The cost of the shirt is $30.79, and the cost of the hat is $19.75.
Now, we add these two amounts together:
\[ 30.79 + 19.75 = 50.54 \]
Now, we subtract the total cost from the amount Britney gave the sales clerk:
\[ 100.00 - 50.54 = 49.46 \]
So, the amount of change Britney should receive is $49.46.
The correct answer is B. $49.46.