わけだ
文法の解説は英語です。
用法
The reason is that; It means that -; That's why -
例文
東京は電車や地下鉄やバスが便利な街なので、車がなくても生活できるというわけです。
Because Tokyo has buses, trains and subways it is a practical city, that is why you do not need a car for the daily life.
あっ、ヒーターが止まっている。寒いわけだ。
Woah, the heater stoped working. The reason is that it is cold.