Subject-Auxiliary Inversion – Why Doesn’t ‘Have’ Agree With ‘He’ in ‘Does He Have It?’

Edit: you are saying the opposite of every English language book. Actually, has is singular, and have is plural! (in the third person, that is.)

Your sentence has a plural subject: economic growth and commercial development.

Because of that, the verb also takes the plural.

When you use A and B as the subject, it is plural.

Consider the following sentences:

Alice has a book.
Bob likes reading.

Now, with and, we get the plural:

Alice and Bob have a book.
Alice and Bob like reading.

I agree with those in the comments, that using "What [were you]/[have you been] doing?" is much more likely to be interpreted by the recipient as rude, or at least intrusive. I can't think of a situation in which I would use either of these phrases unless I was essentially accusing someone of doing something they shouldn't have been.

If I'm interested in what someone has been doing, instead of saying "What were you doing last week?", I might say "What did you get up to last week?", although if the last time I spoke to them was much more than a week ago and there's no specific reason why last week was important, then I'd probably just say "What have you been up to?".

Disclaimer: I'm a native UK English speaker, so some of the above might be a little regional to the UK. I have spent a fair bit of time in the US and understand a decent amount of their regional variations, but I'll let a native US English speaker fill in the gaps if necessary.