Answer
String length=50 ft
Work Step by Step
Act to figure
hypotenuse = string length of kite
Using Pythagoras theorem
$hypotenuse\times hypotenuse =30\times 30+40\times 40 $
$hypotenuse\times hypotenuse =900+1600 $
$hypotenuse\times hypotenuse =2500$
=50
String length=50 ft