Question

Jill and Ben have the same pens Jill has 3 full boxes of pen and 2 loose pens Ben has 2 full boxes of pen and 14 loose pens how many pens are there in a full box

Answer 1

Let x be the number of pens in a box.

Jill : three full boxes of pen and 2 loose pens. 3x + 2
Ben: two full boxes of pen and 14 loose pens. 2x + 14

Jill and Ben have the same pens. 
Jill        = Ben
3x+2    = 2x + 14
3x - 2x = 14 - 2
      1x  = 12
         x = 12

To check:
Jill            =       Ben
3x + 2      =       2(x) + 14
3(12) + 2  =       2(12) + 14
36 + 2      =       24 + 14
           38 = 38

There are 12 pens or a dozen of pens in a full box.