When u see square that means u have to multiply the number by it self.
( 3x + 7 ) * ( 3x + 7 )
3x * 3x = 9x^2
3x * 7 = 21x
7 * 3x = 21x
7 * 7= 49
Now u have 9x^2 + 21x + 21x + 49
Now u have to combine like terms meaning u have to add the number that have the same variable ( x )
21x + 21x= 42x
Answer: E.) 9x^2 + 42x + 49