Looking on the internet deeply has found these results:

I was busy with my studies is the most popular phrase on the web.

i was busy in my studies 111,500 results on the web	I was busy with my studies 121,200 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
But I'm too busy with my studies. I was busy in the back. I didn't hear anything till the police showed up. I was busy in back with a customer. My parents were always busy with studies. He was forever busy in his study. The entire day I was busy in and outside of the house. I've just been so busy with my studies. And my eldest daughter was busy with her studies in Tokyo.	While you were busy minoring in gender studies and singing a capella at Sarah Lawrence, I was gaining root access to NSA servers. My parents were always busy with studies. I've just been so busy with my studies. But I'm too busy with my studies. You're always busy with your study group. I take it you've been too busy with security to study the latest reports from Earth? I was far too busy with my... studies. And my eldest daughter was busy with her studies in Tokyo.

i was busy in my studies

111,500 results on the web

I was busy with my studies

121,200 results on the web

More popular!

While you were busy minoring in gender studies and singing a capella at Sarah Lawrence, I was gaining root access to NSA servers.
My parents were always busy with studies.
I've just been so busy with my studies.
But I'm too busy with my studies.
You're always busy with your study group.
I take it you've been too busy with security to study the latest reports from Earth?
I was far too busy with my... studies.
And my eldest daughter was busy with her studies in Tokyo.