If you're asking about the largest number that can be written with 3 digits in the given base:
• In base 2, the largest number with 3 digits is
111₂ = 1•2² + 1•2¹ + 1•2⁰ = 7
• In base 12, the largest number with 3 digits is
bbb₁₂ = 11•12² + 11•12¹ + 11•12⁰ = 1727
(in base 12, a₁₂ = 10 and b₁₂ = 11)
