Explanation

Using log rules, the expression is log₁₀(2000×400) + log₁₀(25⁴) + log₁₀(20⁵). Writing 2000×400 = 8×10⁵, 25⁴ = 5⁸, 20⁵ = 2⁵×10⁵, this is (5 + 3log₁₀2) + (8 − 8log₁₀2) + (5 + 5log₁₀2) = 18, since the log₁₀2 terms cancel. Hence the value is 18, option (c).