a) 10011₂ = 1 * 2⁴ + 0 * 2³ + 0 * 2² + 1 * 2¹ + 1 * 2⁰ = 16 + 0 + 0 + 2 + 1 = 19
б) 254₈ = 2 * 8² + 5 * 8¹ + 4 * 8⁰ = 2 * 64 + 5 * 8 + 4 * 1 = 128 + 40 + 4 = 172