x is 1000, and the other side of the rectangle is 60 cm.
Area is found by multiplying length by width. Using the sides we know we have
[tex]300=5(\sqrt{x+2600})[/tex]
We divide both sides by 5:
[tex]\frac{300}{5}=\frac{5\sqrt{x+2600}}{5}
\\
\\60=\sqrt{x+2600}[/tex]
To "undo" a square root, we square both sides:
[tex]60^2=(\sqrt{x+2600})^2
\\
\\3600=x+2600[/tex]
Subtract 2600 from both sides:
3600-2600=x+2600-2600
1000=x
Now we substitute this into the side with x:
[tex]\sqrt{x+2600}=\sqrt{1000+2600}=\sqrt{3600}=60[/tex]
