Laszlo Biro's story- Past Continuous & Past Simple

Описание: Laszlo didn't like fountain pens because they were making a mess.
He was writing with a messy pen when he thought of an idea for a better pen.
He was drawing the ballpoint pen design when he got a sudden idea.
While he was working on the design, he imagined a tiny ball in the tip for smooth paper glide.
While they were dealing with a technical problem, they suddenly found a solution.