The expression ax2-bx=0 is? and has the solution x=0

Lets analyze the equation:
ax^2 - bx = 0
x(ax - b) = 0
Therefore if x = 0, the equation holds no matter about a and b:
0(0a - b) = 0
0 = 0

In all honesty, there really is no “work” per say to show. mainly it’s just using the process of elimination. the question is asking which domain(s) would be the most appropriate for the function c(n). n is the number of observed vehicles so right away, 1, 2, and 3 can be eliminated.why? 1, 2 start in the negatives and therefore it is impossible to observe negative cars. so, #4 would be the best answer to the given problem.