Final answer:
The triangles are similar by the SSS similarity postulate because all corresponding sides of the two triangles are in the same proportion.
Step-by-step explanation:
To determine whether the two triangles are similar, we can use one of the similarity postulates or theorems such as the Side-Side-Side (SSS) similarity postulate, the Angle-Angle (AA) similarity theorem, or the Side-Angle-Side (SAS) similarity theorem. In our case, since all three corresponding sides of triangle one (5, 5, 8) and triangle two (7.5, 7.5, 12) are in the same proportion (5/7.5 = 2/3 and 8/12 = 2/3), we can conclude that the triangles are similar by the SSS similarity postulate.