The line crosses the x-axis at (-3, 0) and goes upward because it has positive slope- how could it possibly have negative y intercept?
Your very first equation is wrong: Y/X= M is incorrect because that only applies when the graph passes through (0, 0). What is true is that $\displaystyle \frac{\Delta y}{\Delta x}= M$ or $\displaystyle \frac{y_2- y_1}{x_2- x_1}= M$ where $\displaystyle (x_1, y_1)$ and $\displaystyle (x_2, y_2)$ are two points on the line and $\displaystyle \Delta y= y_2- y_1$ and $\displaystyle \Delta x= x_2- x_1$. Here one point is (-3, 0) (the x-intercept) and another is (0, y) (the unknown y- intercept). You should have $\displaystyle \frac{y- 0}{0- (-3)}= 3$.
No, these questions don't sound stupid- they sound like you are memorizing formulas without understanding what they mean! I know the line is going upward because that is what "slope" means! The slope measures the rate at which the y-value is increasing relative to the x-value. Positive slope means y is increasing, negative slope means y is decreasing.
"for the very last equation y can't equal 9 because the answer will be 3."
What answer? The answer to what question? The last equation is $\displaystyle \frac{y}{3}= 3$. y has to be 9 to satisfy that.