The center of gravity will balance the triangle in the x direction, as well as in the y direction.

The area of the triangle is

You now need a triangle such that

The ratio of the main triangle's height to the base is

You need to have or

The center of gravity will occur along the triangle with the x coordinate equal to 21.2132.

You will need to do the appropriate calculations for the y coordinate.

You want to cut the large triangle so that the upper or smaller triangle is half the area of the larger triangle.