I need help please :) I don't understand how to do it. Thank you ! :)

Step-by-step explanation:

supplement means their addition is equal to 180°

since m<x and m<y are supplement then m<x+m<y=180

and <y supplement to <z (their addition equals to 180°)

since m<y and m<z are supplement then m<y+m<z=180

m<x+m<y= m<y+m<z

m<y cancelled

m<x= m<z

FOR EXAMPLE

Given that <x and <y are supplement

and <y and <z are supplement

if <x= 45°

that means that <y = 135°

so that <x +<y = 180°

45+135= 180 ✓

and <y and <z are supplement

m<y+ m<z = 180°

then m<z= 45°

m<x+m<y= m<y+m<z

m<x +135= 135+m<z

then m<x= m<z = 45°