Answer:
10th week
Explanation:
We have been given that
![S=(120t)/(t^2+100)](https://img.qammunity.org/2019/formulas/mathematics/high-school/bidiu9eiedjcchgrpluksu0hb06m7j7ldz.png)
Now, we have to find t for S= 6
Substituting, the value of S in above equation
![6=(120t)/(t^2+100)](https://img.qammunity.org/2019/formulas/mathematics/high-school/2lxlc5x9f0xjf96gfae7vwuppcnl5zcq8b.png)
Cross multiplying, we get
![6t^2+600=120t](https://img.qammunity.org/2019/formulas/mathematics/high-school/fzpdlutqfrwsm1v15liacxe1zh07ma0g26.png)
Subtract 120t to both sides
![6t^2-120t+600=0](https://img.qammunity.org/2019/formulas/mathematics/high-school/1hmu1hh1w8lxod1u6qwj024vrd8262rf5s.png)
Divide both sides by 6
![t^2-20t+100=0](https://img.qammunity.org/2019/formulas/mathematics/high-school/cd85oa0n5vo0igv0ll9llkhbqaacwvzl9u.png)
We can write this in perfect square as
![(t-10)^2=0](https://img.qammunity.org/2019/formulas/mathematics/high-school/kvbodwtabwdg2yoh9m3iz9b9ix66s8r5at.png)
Solve for t
![t-10=0\\\\t=10](https://img.qammunity.org/2019/formulas/mathematics/high-school/lgh0wkconl8vez5rtrkyqz3mgjwzgfgti1.png)
Therefore, in 10th week, the sale would have been 6.