It looks like you're given a question in slope intercept form.
Which is: y = mx + b, (m = slope and b = y-intercept)
Plug M and the point you know into the equation.
y = mx + b
8 = -3(2) + b
8 = -6 + b
14 = b
Now that you have your y-intercept, add that to the equation along with m, and what you know of the missing value (the point x, -4, you have the value of y, which is -4, so you're looking for the value of x)
-4 = -3x + 14
-18 = -3x
6 = x
So, your missing value is 6. I hope this was helpful and have a grreat rest of your day! ~ Saturns <3
