help ! could someone explain?

Answer:
[tex]\boxed{\sf \ \ KM=10 \ \ }[/tex]
Step-by-step explanation:
Hello,
let 's note JK = a, KL = b and KM = x
in JKL we can write
[tex]a^2+b^2=25^2[/tex]
in JMK
[tex]5^2+x^2=a^2[/tex]
in MLK
[tex]20^2+x^2=b^2[/tex]
So we can write
[tex]5^2 + x^2 + 20^2+x^2=a^2 + b^2=25^2\\\\<=> 2x^2= 625 - 400 -25=200\\\\<=> x^2=100\\\\<=>x=10[/tex]
hope this helps