I believe you meant to say "How many cars did Jeff sell last month one year ago?" at the end. If that is the case, then the answer would be 63. 27+36=63
For this case we have the following equation: Rewriting we have: We raise both members of the equation to the square: Rewriting we have: It's a extraneous solution because equality is not met by substituting x = 10 in the original equation: Answer: The solution is: It's a extraneous solution