\(a)\) \({a^3}.{a^5} = {a^{3 + 5}} = {a^8}\)
\(b)\) \({x^7}.x.{x^4} = {x^{7 + 1 + 4}} = {x^{12}}\)
\(c)\) \({3^5}{.4^5} = 3.3.3.3.3.4.4.4.4.4\)
\( = (3.4).(3.4).(3.4).(3.4).(3.4).\)
\( = 12.12.12.12.12 = {12^5}\)
d) \({8^5}{.2^3} = {8^5}.8 = 8^{5+1}={8^6}\)