Answer:
add x to both sides. once you do this, you will get x+y=15
Answer:

Step-by-step explanation:

The answer is 6. Sorry, I don't know why though.
It'd be best if you'd stick to symbols. My interpretation of what you've typed here is 20x - 20x^2 + 5x^3. In descending order by powers of x, that gives us
5x^3 - 20x^2 + 20x.
f(x) = 2x + 1
y = 2x + 1
x = 2y + 1
x - 1 = 2y
2 2
¹/₂x - ¹/₂ = y
The answer is A.