Answer:

Explanation:
We have been given a perfect square trinomial
. We are asked to fill in the missing blank.
We know that a perfect square trinomial is in form
.
We can rewrite terms of our given expression as:


We can see that the value of a is 2x and value of b is 7, so
will be:

Since we are asked to give numerical answer, so the missing value is 28 for our given perfect square trinomial.