Rewrite Expressions

Hailey just had lunch at the Sushi Palace, and she wants to leave an 18% tip. She writes the expression b + 0.18b to compute her bill with a tip, where b is her bill before the tip.
Question 1
Which expression is equivalent to Hailey's expression?
Responses
A 1.18b

1.18b
B 0.18(2b)0.18(2b)
C 1.18(2b)1.18(2b)
D 2(1.18b)