13.05 completing the square:

x^2+20x=10

x^2-4x=8

x^2+5x=3

x^2-9x=5

2x^2-48x=10

x^2+2x=8

x^2-6x=16

x^2-18x=19

x^2+3x=3

x^2+7x=8

The way these equations are arranged helps. 
First only deal with the left handside. 

X^2+20x= (x+a)^2 -b where we are looking for a,b
You need to know the general formula for (x+a)^2=x^2+2ax+a^2
20x = 2*10x so a will be 10
(x+10)^2= x^2+20x+100

Now lets look at the original question: 
X^2+20x=10
we know now that (x+10)^2= x^2+20x+100
Thus X^2+20x=(x+10)^2 -100
So X^2+20x=10 becomes

(x+10)^2 -100 =10
(x+10)^2=110
For the other question you need to follow the same logic.

Do the inverse operation