The Pythagoras Theorem:
the base squared and height squared added is equal to the hypotenuse squared.
so
(x+6)² + (x+3)²= (x+9)²
x²+36+12x+x²+9+6x = (x+9)²
2x²+45+18x=x²+81+18x
x²=36
x=√36
X= 6
now
(x+6)= 12
(x+3)=9
(x+9)=15
haha sorry correct it pls