If you have several different sized pizzas, you can compare their areas. So the area of a pizza is the length of the crust (circumference) divided by two times the distance from the edge to the middle (radius). Mathematicians use a special number called pi to calculate the circumference of a circle.
15.5-3.5=12. this is how many hours he has worked already.
12/1⅓=9. this is because how many hours he has worked per how many hours he worked per day to show how many days he worked
the answer is 9 days.
12hours * 1day/1⅓ hours
^^ignore that if it doesn't make sense, but basically the hours will cancel and you'd be left with days as your only unit to show why you would divide 12 by 1⅓
hope this helped!