All proportion problems involve two descriptions in two different ways.
This problem asks for height, and one decription is
height of person and height of ceiling
another is height before shrinking and height after shrinking.
Once you have determined this, you write a table like this
first descripton first descripton
way 1 way 2
For your example, that is
height of person height of ceiling
height before 68 96
height after 12 c
From this table you can read off the proportion by placing fraction bars in the same place and an equal sign in between the two fractions. Whether you go across or down doesn't matter. That is you can get either
68/12 = 96/c by creating the
68/96 = 12/c by creating the
In fact you can even go from right to left or bottom to top. The important thing is just that you do it the same way in both cases. That is you could also get
12/68 = c/96
96/68 = c/12
Try it out. Solve all four equations for c. You will get the same answer each time. So the most important thing is to set up your table correctly.