Step-by-step explanation:
[tex]m\angle X+m\angle Y+m\angle Z= 180° \\ \therefore \: 34 \degree+m\angle Y+26 \degree = 180 \degree \\ \therefore \: m\angle Y+60 \degree = 180 \degree \\ \therefore \: m\angle Y = 180 \degree - 60 \degree\\ \\ \huge \red{ \boxed{\therefore \: m\angle Y = 120 \degree }} [/tex]
