What is (4) + (25)?

The product rule for logarithms says $\log a+\log b=\log(ab)$. So $\log4+\log25=\log(4\cdot25)=\log100$. A common logarithm has base $10$, and $10^2=100$, so $\log100=2$, choice J. Choice H ($29$) adds the numbers inside the logarithms, $4+25$, which is not a valid rule. Choice G ($100$) is the argument of the logarithm rather than its value. Choice F ($1$) would be $\log10$. The product rule turns a sum of logarithms into the logarithm of a product, so look for numbers that multiply to a power of the base.