Thank you for the opportunity to help you with your question!

Function of "y a function of x" (denoted y = y( x)

y-varies according to whatever value x takes on. A causal relationship is often implied (i.e. "xcauses y"). or varies directly. In this particular question

we can find the value of y to determine if x causes y

x2+2y=-4

2y=-4-x2. this does not give the correct answer of y

B -y=2-x2

B is the correct answer

Please let me know if you need any clarification. I'm always happy to answer your questions.