They are similar by the Side-Side-Side Theorem.
The smaller triangle is 3/4 of the second triangle:
90/120; divide each by 10, = 9 / 12 which simplifies to 3/4
135/180; divide each by 15, = 9 / 12 which simplifies to 3/4
117/156; divide each by 13, = 9 / 12 which simplifies to 3/4
