It is given in the question that,

Two sides of a triangle are 12 cm and 15 cm respectively

We know that,

In a triangle, the sum of the length of either two sides of the triangle is always greater than the third side

In a triangle, the difference of the length of either two sides of the triangle is always lesser than the third side

The third side will be lesser than the sum of these two sides:

12 + 15 = 27 cm

The third side will be greater than the difference of these two sides:

15 – 12 = 3 cm

Hence, Two measures are: 27 cm and 3 cm