Respuesta :

7 is to 4 as 21 is to x 

Since 21 is (3)(7); (3)(4) = 12 

12 stickers
First of all, you need to divide 21 by 7 to get 3

Then you can times the 3 by 4 to get the number of stickers Jenna has:
3*4 = 12

Hope this helps! :)