Question: x2 + 10x + 35 + 0 (complete the square)
Where did you get this expression from? Are you sure there is no typo? The '+' sign and '=' sign on a keyboard are on the same key and can easily be mis-hit.
You also have x2, rather than x^2, so I am assuming a typo.
If you don't have an equals sign then it is an expression, rather than an equation, but you can still complete the square.
Completing the square is a procedure that applies to an expression.
But in an equation, you have expressions on either side of the equals sign, so completing the square can be applied to an equation also
Assuming the expression is the equation shown below ...
x^2 + 10x + 35 = 0
x^2 + 10x + 25 + 10 = 0
(x + 5)^2 + 10 = 0