Let Issac work for x hours, and Ruby works 8 hours more than of Issac, so Ruby work for hours.
And Svetlana worked four times of Ruby, therefore Svetlana worked for
And total hours they worked together is 136. That is
So Issac worked for 16 hours, Ruby worked for 24 hours and Svetlana worked for 24 times 4 equals 96 hours .