Merhaba.

In an online language course I´ve learned that a way to ask "how often?" (eg. how often do you do something?) is ne sıklıkta? (literally: in what frequency?)

And now I wonder, can I apply this pattern in other examples. When, let´s say a policeman stops me for speeding and I want to ask "How fast did I drive?", can I say Ne (kaç?) hızda sürdüm?

And also in these examples, can ile be used instead of -da? Frankly it´s a more natural way in such expressions for me, because in my native language we also use instrumental case (with) in this kind of questions

Hey, this question seems quite easy.. Ain´t there anyone willing to answer?

I thought 

how often was= ne sıklıkLA

and, how fast= ne kadar hızlı

my try

Selam

If you want to use "kaç", You can say:

"Kaç kilometre (km) hız yaptım?" 

"Hız yapmak" is an informal phrase; however, it´s a phrase in use. No need to be too formal. It is okay.

"Ne kadar hızlı sürdüm?" is also true, but "Kaç km..." is some more direct question.