The solution to a system of (linear) equations is the point where the graphs intersect. Consider two parallel lines. By definition, two parallel lines never intersect each other, but all pairs of non-parallel lines will eventually intersect. That means they will also have a solution.
Let's consider what makes a line parallel to another line. It basically looks identical, having the same steepness (slope), but the graph is just shifted over. That is, a parallel line would have the same slope and a different y-intercept. For our equation

, or

in slope-intercept form, a parallel line will be of the form

.
That describes the form of a parallel line, which we do not want. Any other line, however, will give a solution to our system, so we merely want a line where the slope does not equal 2.
We can have any equation of the form

.
45/x =15/100
Cross multiply
15x=4500
Divide both sides by 15
X=300
300 total cars on parking lot
Answer:
(a) see attachment
(b) E(x) = 226/105
Step-by-step explanation: see attachment
If you are working with time or days, you can't put in a negative value because if you are doing an experiment, you can't go back in time to do that experiment to gather data. (Time for the most part considered to be an input value so that's why I used it as an example.)