Explanation: When you are typing an equation into a cell, the first thing that must be entered is option (4) an equal sign (=). In Excel, the equal sign is used to indicate that the contents of the cell should be treated as a formula or equation. By starting with an equal sign, Excel understands that you are entering a calculation or function. After entering the equal sign, you can then proceed to input the formula or equation, which may include cell references, operators, functions, and other elements.