84 the process is shown in the following picture
First box is 14 under 28 is 7 under 42 is 10.5 on top of 1,208 is 30.2 under 120.8 is 4,832 and under 15.1 is 604
Hope I am not to late please hit thanks if you get it right !
The answer is a. Because at approximately 17 weeks the two lines meet.
This will be commutative property. with the help of the equation a+b=b+a