SOLUTION: Julio needs to draw a line 15 cm long. He does not have a ruler. He does have several sheets of paper that measure 28.0 cm by 21.5 cm. How can he use these papers to draw his 15

Lay two sheets sideways, one above the other,
with their 28cm sides together, like this:



This makes a rectangle which is 2x21.5cm 
or 43cm tall. So AB = 43cm.

Now place a third sheet upright on top of those
like this:



Now since AB = 43cm, and BC = 28cm,
then AC = AB - BC = 43cm - 28cm = 15cm.

Edwin