Answer:
3√13
According to the Pythagoras Theoram,
z² = y²+(9)²--------> (1)
Again , (13)²=x²+z²
so, z² = 169-x² ----------> (2)
Now, x² = y²+(4)²
=> y² = x²-16------>(3)
Comparing 1 and 2
y²+81 = 169-x²
From eq 3
x² -16 +81= 169-x²
2x² + 65 = 169
2x² = 169 -65
2x² = 104
x²= 104/2 = 52
From eq 2
z² = 169-x²
z² = 169-52
z² = 117
z= √117
z= 3√13