logₐ(ab³) = logₐ a + logₐ b³ = 1 + 3 logₐ b
log<0xE2><0x82><0x99> a = 1/7 => logₐ b = 1 / (log<0xE2><0x82><0x99> a) = 1 / (1/7) = 7
1 + 3 · 7 = 1 + 21 = 22