Find x if y=-2 4x-6/y=15a. 9/2b.5c.3d.-6/23

X means everything in algebra. It is a variable, which means that its meaning changes based on context. For example, x could be time, but it could also be cars. x is what all Mathematicians chase after and it is also the greatest tool at their disposal. x is generally called an independent variable because its value determines the output of a function. y, on the other hand, is the result of fooling around with x. It's a dependent variable, which means that y changes when x changes. 

Take, for instance, the following function: 
y = x + 3 

Let's set x = 3. 
y = (3) + 3 
y = 6 

As you can see, what we input as x determines what y outputs.