Given expression is 
 .
.
Question says to write that in form of 
 .
.
That can be done by factoring 
 or apply the identity
 or apply the identity 
 .
.
I'm going to use factor method.
compare given problem 
 with standard polynomial
 with standard polynomial 
 . we get:
. we get:
a=4, b=36, c=81
Step1: find a*c which is 4*81=324
Step2: find two numbers whose product is a*c and sum is b. That means find two numbers whose product is 324 and sum is 36. Required numbers are 18, 18.
using these two numbers we can break middle term 36p as 18p+18p





Hence final answer is 
 .
.