26.
$$2{\log _{10}}^5 + {\text{ }}{\log _{10}}8{\text{ }} - \frac{1}{2}{\log _{10}}4 = ?$$

27.
$${\text{If }}{\log _a}\left( {ab} \right){\text{ }} = {\text{ }}x{\text{, then }}{\log _b}\left( {ab} \right){\text{ is - }}$$

28.
$$\eqalign{ & {\text{If}}\,\,{\log _{10}}2 = a\,{\text{and}} \cr & {\log _{10}}3 = b,\,{\text{then}} \cr & {\log _5}12 = ? \cr} $$

29.
$$\eqalign{ & {\text{If}}\,{\log _{10}}125 + {\log _{10}}8 = x, \cr & {\text{then }}x\,{\text{is equel to}} - \cr} $$

30.
$$\eqalign{ & {\text{If }}{\log _5}\left( {{x^2} + x} \right) - {\log _5}\left( {x + 1} \right) = 2, \cr & {\text{then the value of }}x{\text{ is - }} \cr} $$