4x - y = 5 --> 4x = y + 5
substitute
4x + 4y = -4
(y + 5) + 4y = -4
5y + 5 = -4
5y = -9
y = -1.8
solve x
4x = y + 5 = -1.8 + 5 = 3.2
x = 3.2/4 = 0.8
the area of a square = length*length =3a*3a=9a^2
5+2=7, so the first blank is 2.
For the second blank, you just need two numbers in the box that when added, equals 7. (So 1,6 or 3,4)
You would subtract x from each side. It would then be 3y=-x-15. Then you would divide all of the equation by 3. Your final answer would be y=-3x-5.
You can see that there are 6 rock CDs, over a total of

So, the ratio of rock CDs over the total number of CDs is

Which is 15%.
So, yes, the answer is A