Let the sides be called x, y and b.
1) x = b - 2
2) y = b + 8
3) 30 < or = x + y + b
substitute eqs (1) and (2) into eq(3):
30 < or = (b - 2) + (b + 8) + b
30 < or = 3b + 6
subtract 6 from each side:
24 < or = 3b
divide both sides by 3:
8 < or = b
or
b > or = 8