How is this math problem done?

I'm reading a book and it shows how the problem was done but not explain. Here's the question. After eating 25% of the jelly beans, Brett had 72 left. How many jelly beans did Brett have originally. And here's how it's show on how it's done. Step 1: x-0.25x=72. Step 2: 0.75x=72. Step 3;Answer: x=96. How was from step 2 to the final answer done?