The answer is b, -11.
plug in 3 as the input and solve.
I would like to help but i dont know either

Sounds like that to me but that is symbolically showing of that's what your teacher means as mathematical sentence
Answer:
£4.65 is her bill
Step-by-step explanation:
Here, we firstly need to calculate the unit price of a pint
Mathematically, in this case, that will be 3.72/12 = 0.31
ordering 3 extra pints means she would be buying a total 15
The price of this will be;
0.31 * 15 = £4.65
Answer: (D) 
Explanation:

Just a note on writing down these expressions: I recommend using parentheses whenever you can to avoid misinterpretation. An expression 1/x-1/y / 1/x+1/y could be interpreted by someone as 1/x-(1/y / 1/x)+1/y, which is a different thing.