This can be easily solved, especially with a calculator.
With the calculator, you can find that [tex]\sqrt{42}[/tex] is about 6.4807.
Multiply that by 2, you get about 13 inches.
If you can't use a calculator, then you can just estimate. Since we know that [tex]\sqrt{36}[/tex] is 6 and [tex]\sqrt{49}[/tex] is 7, [tex]\sqrt{42}[/tex] is in between them, so you can just say somewhere around 6.5.
Multiply 2 * 6.5 and you get 13 inches.
