As you can see there's a lot of possible roots. Luckily, p = 1 so that means we simply need to list the factors of q (the plus and minus versions)
The possible rational roots are listed above when I listed all the possible factors of q. Those are the possible x values that make f(x) equal to 0. You need to plug each of those values into f(x) to see which result in 0. It turns out that only x = -4 leads to f(x) = 0 being true. None of the other possible rational roots are actual rational roots.
Answer: $336 explanation: 60% is equal to .6 so just take $210 and multiply that by .6 to get $126. Now, just take $126 and add it to $210 and you have $336.