The overall cost is $50.33. you now subtract out the prices you know. The easiest way to do that is to add them up; 17.97+25.49. That is 43.46.
The next step is to subtract 43.46 from 50.33. 50.33-43.46=6.87. That is the price of all the pairs of socks put together.
to find out how much one pair is, you then divide 6.87 by 3. That is 2.29.
The answer is $2.29
I hope this helps!
Let numbers of books be 'b' and numbers of CDs be 'c'
We can set up two equations:
Equation [1] ⇒

Equation [2] ⇒

We are solving for the number of books and the number of CDs bought
When we have two equations in terms of two different variables;

and

, that we need to solve, then this becomes a simultaneous equation problem.
First, rearrange Equation [1] to make either

or

the subject:


Then we substitute

into Equation [2]






Now we know the value of

which is

, substitute this value into

we have

Answer:
Numbers of books = 13
Numbers of CDs = 7
It is the last answer choice