I plugged in 30 for the number of desks…

For the question 8 about plugging in
I plugged in 30 for the number of desks, and so e=25 and c=48. But, it didn’t match any of the answer choices. I don’t understand what went wrong. I checked it over and over again. Pleease help aaaaa

For the official practise test 2, section 3, question 4 is listed as a “plugging in” question. So when I tried it out, I substituted 1 for both variables a and b…

For the official practise test 2, section 3, question 4 is listed as a “plugging in” question.
So when I tried it out, I substituted 1 for both variables a and b. That easily allows me to pick option A.
However, one of your rules was to never plug in the values 0 and 1, yet 1 was a viable option for this question.
So how can I know when plugging in 1 will be okay and when it’s a bad idea? Also, is my method correct for this question or would you suggest another way? Thanks so much!