so you got
z²+y²=25² and
17²+x²=z²
x²+6²=y²
nice, so we have z² and y² all in terms of x
17²+x²+x²+6²=25²
2x²+289+36=625
2x²=300
x²=150
x=5√6
if we input back to find y and z
17²+x²=z², 287+150=z², √439 =z
x²+6²=y², 150+36=y², √186=y (not simplifying because no graphing calculator, so just eimplify yourself)