How can a problem with extra information be difficult to solve

Extra information is something called a "red herring".  What a red herring does is distracts your attention from what you need to know.  This happens because humans thinks it needs to use all of the provided information, even if you only need half of it.  My physics teacher always mentions that the acceleration of gravity is 9.81m/s^2 just for this purpose, even if gravity doesn't matter in the calculations.