b₃ = 3
b₁ * q² = 3
b₁ * b₂ * b₃ * b₄ * b₅ = b₁ * b₁ * q * 3 * b₁ * q³ * b₁ * q⁴ = 3 * b₁⁴ * q⁸ =
= 3 * (b₁ * q²)⁴ = 3 * 3⁴ = 3 * 81 = 243
