Answer:
a - 2
Step-by-step explanation:
Perimeter = side 1 + side 2 + side 3
So
6a + 3 = 2(a + 3) + (3a - 1) + side 3
side 3 = (6a + 3) - (2a + 6) - (3a - 1)
side 3 = 6a - 2a - 3a + 3 - 6 + 1 = a - 2
correct answer right here
