For complicated equations in Word, you may want to use the Equation Editor. Assuming you have the Equation Editor installed, you can launch it from Word by choosing Insert | Object, selecting the Create New tab, finding Microsoft Equation 3.0 in the Object Type list, and clicking on OK.
For simple equations like the one you describe, you may want to fall back on Word's Equation field. A Word field translates a command into a result. If you know the command, it's easy to enter the field. First type Ctrl-F9 to enter the field code markers (which look like curly brackets). Then enter the field commands between the markers (see Figure 3). In this case the field would read Eq e\s\up2(7x)\s\up4(2). This tells Word to create an equation by entering an e, followed by a superscript that is 2 points higher, using the text 7x. Then enter a superscript that's a total of 4 points higher than the e, using the text 2.
For the complete list of equation field commands in Word, choose Help than chooseMicrosoft Word Help. Select the Answer Wizard tab and type Equation field as the item to search for, then click on Search. In the Select topic to display list, choose Field codes: Eq (Equation) field and explore the options.