20 ? i’m a little confused on the “2x” part

whatever you do to one side, you must do to the other side to keep the equation balanced.

in order to isolate the variable (x), you need to divide by 2.  Since you are dividing the right side by 2, then you must divide the left side by 2.

-10÷2  = 2÷2x

-5  = 1x

-5 = x

sample answer: you can determine whether each element of the domain is paired with exactly one element of the range. for example, if given a graph, you could use the vertical line test; if a vertical line intersects the graph more than once, then the relation that the graph represents is not a function.