42 baseball caps
Since 84% = 84/100 , and 50 is 1/2 of 100 we can think of 84% of 50 being half of the value of 84% of 100. So 84/2 = 42
There are other ways of solving such as multiplying 50 by 0.84, however I believe that how I solved it was the easiest way for this specific problem :)
