1️⃣ Head to the add new step element in your query builder, and select columns.

2️⃣ Select add new column from the drop down box.

3️⃣ Name your new column and head down to the Enter your formula box. You will see existing columns are suggested below.

4️⃣ Format your formula as follows: column1 * column2.

5️⃣ Hit Done!