The 4 m board's center of mass is 2 m so the pivot point is somewhere between Tasha and 2 m (if you draw a picture it's going to make this clearer)
The mass of Tasha * her distance from the pivot point = the board's mass * distance from the pivot point.
Let d1 be the distance Tasha is from the pivot point. The board's center of mass from the pivot point is 2 m - d1
20 kg * d1 = 10 kg * (2m - d1)
Solve for d1, you should get 2/3 of a m for the distance Tasha is from the pivot or support point. The center of mass for the board is 1 1/3 m from the support point.
