Answer:
D
Step-by-step explanation:
The expression is 
We can follow the rule of "PEMDAS" here.
PEMDAS = Parenthesis, Exponents, Multiply, Divide, Add, Subtract
So, we first need to deal with Parenthesis. Next,
There aren't any exponents, so we deal with Multiplication of 7 and 3.
Then addition/subtraction.
Hence, the first step, from the answer choices, would be D, multiply 7 and 3