log₃₀ 8 = 3log₃₀ 2.

log₃₀ 30/2 = log₃₀ 15

log₃₀ 30 - log₃₀ 2 = log₃₀ (3*5) = log₃₀ 3 + log₃₀ 5

1 - log₃₀ 2 = a + b

log₃₀ 2 = 1 - a - b

Hence, log₃₀ 8 = 3(1-a-b)