Find the value of y when x equals -7. -3x+6y=-21

You would substitute -7 wherever you see the x symbol

-3 x -7 +6y=-21
21+6y=-21

then you would move the 21 to the other side and when you move it the sign would change from a +21 to a -21.
so you would be left with
6y=-21-21
6y=-42

then you would take the 6 over and because it is being multiplied to the y on one side, it would divide on the other.

y=-42/6
y=-7

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.