Hey can you me posted picture of question: )

The roots are:
and

Explanation:
First, we will need to expand the bracket on the left and then put teh equation i standard form which is:
ax² + bx + c = 0

This can be done as follows:
(x+5)² = 10
(x)² + 2(x)(5) + (5)² = 10
x² + 10x + 25 - 10 = 0
x² + 10x + 15 = 0

By comparison, we can find that:
a = 1
b = 10
c = 15

Now to get the roots, we would need to use the quadratic formula shown in the attached image.

By substitution, we would find that:
either x = 
or x =

Hope this helps :)

It would be 18 cm