SAT Practice Test 7: Math Section 1: Question 20. Math Module 1. S1Q20

Here's how to do Question 20 from the first math section of SAT Practice Test 7.
This problem sucks. It's one of the two stupid hard problems you will see in every first section of every practice SAT and every real SAT. It takes a lot of careful work.
The key here is to see that the language "one solution to the given equation" means that x = 8 - square root k / 4. All you gotta do is replace each x with 8 - square root k / 4 and work through the algebra. That sounds easier than it is. The good news is that, like always, the square-root stuff falls out and you end up with a pretty simple algebraic equation at the end.