`log_4 x + log_2 x` `= 6 ⇔ (log x)/(log 4) + (log x)/(log 2)` `= 6` `:. (log x)/(2 log 2) + (log x)/(log 2)` `= 6 ⇔ 3 log x` `= 12 log 2` `or log x` `= 4 log 2 ⇔ log x` `= log ^24 or x = 2^4` `= 16.`