Please, in the future, post just one problem at a time.
Looking at Problem #1:  The line intersects the y-axis at (0,-3) and intersects the x-axis at (1,-1).  At least, this is what I see; your graph is small.
                                                                           -3-[-1]
The slope of that line is then  m = rise / run = ------------ = +2.
                                                                            0 - 1
                                       [change in y]
Slope = m = rise / run = --------------------
                                        [change in x]
        
             
        
        
        
18;45 = 9
24;16 = 8
I hope this helps
        
             
        
        
        
We know that 16 cups are in 1 gallon
We also know that 10 servings = 2 cups
Now that means 80 servings = 1 gallon
That means we need 320 / 80=4
It is A 4 gallons 
Hope this helps