Answer:
4 feet by 3 feet
Step-by-step explanation:
I think your question is missed of key information, allow me to add in and hope it will fit the original one.  
Please have a look at the attached photo.  
My answer: 
 width-to -height ratio of 16:9
Let analyse all possible answers: 
16 divided by 4 is the same as 9 divided by 3 => it is true 
16 divided by 28 is different as 9 divided by 21 => it is wrong 
- 48 centimeters by 27 centimeters
16 divided by 48 is different as 9 divided by 27 => it is wrong 
16 divided by 26 is different as 9 divided by 219=> it is wrong 
We choose A. 
Hope it will find you well.