Two similar cones have heights 5 and 20. what is the ratio of their volumes?

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.

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?

Precalculus question, image attached.