Hi! :)
The answer is A, here's why:
When tipping at a restaurant, first you need to figure out how much you're tipping. You need to move the decimal left 2 places on how much you tip. So for 20%, you get .20
Then to figure out how much to tip for 20%, you would multiply that .20 by how much the bill was and that's your tip. So .20*30=6. Your tip should be 6 dollars, and the formula for that is t=.20b