12+4+9+13+7+11+5+2+_+_ /10= 8
x10 both sides
12+4+9+13+7+11+5+2+_+_=80
63+_+_=80
-63 both sides
_+_= 17
any two numbers that add up to 17 can go in the planks
7,10
I think 1 is =
2 is =
3 is >
4 is =
5 is =
But I am really not good at math, so I hope I got them right for you!
-Twix
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 .