ANSWER
225/4
EXPLANATION
To complete the square we want to write a part of the equation in the form:
[tex](a+b)^2=a^2+2ab+b^2[/tex]
The second term squared is the one we have to add to the equation in order to complete the square.
In this case, the coefficient of x is 15, so b is:
[tex]b=\frac{15}{2}[/tex]
And b²:
[tex]b^2=\frac{225}{4}[/tex]
If we add 225/4 to both sides of the equation:
[tex]x^2+15x+\frac{225}{4}+7=\frac{225}{4}[/tex]
We complete the square:
[tex](x+\frac{15}{2})^2+7=\frac{225}{4}[/tex]
