Find the value of x that makes N the Incenter of the triangle

What is the value of x when x + 7 = 21?

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.

Isaac wants the equation below to have no solution when the missing number is placed in the box. which number should he place in the box?