How fast are you going? Wow, you're going 300 kilometers an hour!
What's your speed? You're doing 300 kilometers an hour! That's crazy!
ーHow fast are you going? Wow, you're going 300 kilometers an hour!
「今何キロ？わあ３００キロも出てるよ！」
車などで何キロで走っているのか聞く時に How fast are you going? と言えます。
ーWhat's your speed? You're doing 300 kilometers an hour! That's crazy!
「今何キロ？３００キロ出てるよ！すごい！」
What's your speed? でスピードを聞くこともできます。
ご参考まで！
カナダ 
