PLEASE HELP ME. Can't Get Formulas In Word To Work?

I know how to use formulas in EXCEL and I know WORD isn't EXCEL. But I'm trying to enter a very simple formula into a table in a WORD document to calculate simple macro-nutrients. The formula is very simple. Each gram of carbs is 4 calories. I'm just trying to enter a formula that automatically multiples the number of carbs by 4 so I don't have to manually do the math on my own every time. As you can see in my screenshot, I got it to work by entering (=B2*4). The problem is the formula doesn't stay there. It instantly vanishes once entered. So if I change the number of carbs from 100 which is 400 calories, to 200 which is 800 calories, the formula doesn't automatically update the total calories because the formula disappeared once entered. I just want to know if I can enter the formula in a way which causes it to permanently stay in the cell so it always updates the total calories whenever I change the number of carbs? Just like EXCEL always does? And how to do that? If it's not possible, that's okay. I will simply consider going back to EXCEL then.