31. Vietnamese students are obligated to wear uniforms when they go to school

⇒ Vietnamese students have to wear uniforms when they go to school

( have to: phải )

32. Tippping/ not/ custom/ Viet Nam/ so/ you/ not/ have/ tip/ if/ don't want.

=> Tipping is not a custom in Viet Nam, so you don't have to tip if you don't want to.

( clause, so + clause : ..., vì vậy,... )

31. Vietnamese students have to wear uniforms when they go to school. 

 Be obligated to = have to 

32. Tippping/ not/ custom/ Viet Nam/ so/ you/ not/ have/ tip/ if/ don't want. 

=> Tipping is not a custom in Viet Nam, so you don't have to tip if you don't want to. 

Trans: Cho tiền tip không phải là phong tục ở Việt nam, vì thế bạn chẳng cần phải cho tiền tip nếu bạn không muốn.

Nếu được thì cho mình ctlhn nhé, cảm ơn ạ