Explanation

The equation gives log₁₀(100001 − 4ˣ) = 5 − x, so 100001 − 4ˣ = 10⁵⁻ˣ. Trying x = 0: LHS = 100001 − 1 = 100000 = 10⁵ and RHS = 10⁵, which matches (and 100001 − 4⁰ > 0). Hence x = 0, option (a).