Devaughn is 13 years older than sydney. the sum of their ages is 77 . what is sydney's age?

Can someone me with this problem . show your work .

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.

00 points ! missy’s rotation maps point k(17, –12) to k’(12, 17). which describes the rotation? 270° counterclockwise rotation 90° counterclockwise rotation 90° clockwise rotation 180° rotation