(a)
Let's assume
the range of the lengths of the skirts is t inch
now, we are given 
to change hems either up or down 2 inches
so, total change in length should be 2
so, we will have right side =2
the length of the skirts is 20 inch
this will be either greater or lesser to length of skirts 
so, the difference between them will be t-20
so, we get 

(b)
now, we can find range 
firstly, we will break absolute sign 
 for t<20
 for t>20
because value of |t-20| must be positive 
so, we get 

Multiply both sides by -1


Add both sides by 20



Add both sides by 20


so, the range of the lengths of skirts is 
18 in to 22 in..........Answer
(c)
Firstly, we will find difference in height of the model 
5 feet 9 inches 

6 feet =

now, we can find difference in height 

and we are given 
difference in length of skirts =2 in
so, the difference in height is greater than the difference in length of skirts
so, the answer is NO