Math instructors teach students about the Order of Operations, a specific set of steps you must take to solve a problem like that. Sally is the star of an often-used mnemonics device that students use to remember the acronym for those steps.
The steps are summarized as PEMDAS, which stands for Parentheses, Exponents (Powers and Square Roots, etc.), Multiplication and Division (left-to-right), Addition and Subtraction (also left-to-right). The phrase that helps students remember the steps is Please Excuse My Dear Aunt Sally.
There's another and perhaps easier way to learn your PEMDAS: download the Order of Operations app for your Android phone. The app includes a explanatory video, 50 practice questions, timed questions, flashcards, and a timed game.
The app is free and available in the Google Play Store. Your Aunt Sally would be would be proud of you.