Refer to the attached image.
Let the width of the border be 'x' inch.
Area of border = Area of rectangle ABCD - Area of rectangle PQRS
Area of rectangle ABCD = 

= 

= 
 square units.
 square units.
Area of rectangle PQRS = 

= 

= 117 square units.
So, area of border = 
 
 
As it is given that the area of border is 48 square units.
So, 



So, the complete equation is 
 .
.
Now, we will find 'x' in the equation 
 ,
,


(x-1) (x+12)=0
So, x = 1 or x = -12
Width can'not be negative.
So, x = 1 .
Therefore, the width of the border can'not be 2.5 inch.
Therefore, the width of the border is 1 inch.