$a)$

$3^2+4^2=w^2$

$9+16=w^2$

$w^2=25$

$w=5$

 

 

$b)$

$x^2+5^2={13}^2$

$x^2+25=169\mid -25$

$x^2=144$

$x=12$

 

 

$c)$

${0,6}^2+{0,8}^2=y^2$

$0,36+0,64=y^2$

$y^2=1$

$y=1$

 

 

$d)$

${21}^2+z^2={29}^2$

$441+z^2=841\mid -441$

$z^2=400$

$z=20$