Need help with question 16 and I need work please and thanks be correct

(9x-5) - (x+12) what’s the answer and also explain how to do it i need it for a test tomorrow

Nine more than four times a number is the same as one less than twice the number. find the number?

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.