X+0.5X= 15 or 16.

Solution: X= 10 or 32/3.

16-0.5x 10 = 1 1；

15-0.5x(32/3)=29/3。

So the waist length of an isosceles triangle is 10 or 32/3cm, and the base length is 1 1cm or 29/3cm.