Find all solutions to the equation: cos x = sin x

Alicia puts $400 in a bank account. each year the account earns 5% simple interest. how much money will be in her bank account in six months?

Ineed to know the answer to this algebra question.

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.