To find why he would do this, we need to understand what all the possible first steps are in this equation.
You could add 4 to both sides.
You could subtract 4 from both sides.
You could subtract 5x from both sides.
You could subtract 6x from both sides.
Any of these work. In Bernard's case, he added 5 negative x tiles, meaning he subtracted. C and D already make no sense, but allow me to further explain. By him subtracting 5x from both sides, the equation turns into:
-4 = x + 4
By this point, he can just subtract 4 from both sides to find the value of x. But the question asks for why he did the first step. Therefore, it would be A.
