Keep in mind units and it will make sense
20(34)(4*6) = ?
Since the line is going from the top left to the bottom right, the slope is negative so A and B are possible answers.
the line crosses the y axis at -1
B is the option that ends with -1
therefore your answer is B. y = -2x - 1
I'm pretty sure you are asking for the value of b. Let's actually write it and then solve it:

Solving for b yields:

So,
b = 19.59. If you want the answer in simplified radical form, we can also do that:

So,
b = 8√6 = 19.59