Answer:
m4{=100 is the answer,,,,,,
6x+21+15-2x
4x+36
hope this helps...
B)Emily either switched the signs for no reason or solved it in the incorrect order
C) The sudent solved the equation in an incorrect order. Emily solved the first, then third, then second, which was the incorrect order. Edgar solved the thirst root, then second, then third, thus he is correct.
Option C: The solution set is 
Explanation:
The expression is 
Now, let us find the solution set.
Switch sides, we get,

Dividing by 2 on both sides, we have,

Thus,
Hence, the above expression becomes,

Simplifying, we get,

Applying the log rule, we get,

Simplifying, we have,

Applying the log rule, we have,

Thus, the solution set is 
Hence, Option C is the correct answer.