We will start working backwards from 8.10pm. Firstly, we will start on the 2nd blouse that took 2h 55mins to complete. We will subtract 10mins from 8.10pm to make it 8.00pm. Now we are left with 2h 45mins to work with. From there, we will minus 2 hours from 8.00pm which will give you 6.00pm. Next, we will minus 45 mins from 6.00pm to give you 5.15pm. That is the time she started to sew the 2nd blouse.

Now we will move on to the 1st blouse which took 3h 40mins complete. Our current time is 5.15pm and we will minus 3hours to get 2.15pm. Now we are left with 40mins, to make it easier, we will first minus 15mins to get 2.00pm. 40-15 = 25 mins, so we are left with 25mins now. Taking away 25mins from 2.00pm gives you 1.35pm. So that is how you get the time she started sewing.