This is because we start with the slope of 6. This is because it is the slope of the original equation (the number attached to x) and parallel lines have the same slope. Then you can use that along with the point to find the y intercept using slope intercept form (y = mx + b)
y = mx + b 10 = 6(4) + b 10 = 24 + b -14 = b
So -24 must be the number at the end of the equation, making a the right answer.
