Question 1241
 Apply log (base 10) on both sides, we have

 log 5^3x = log 3^(x+4),

 Use log a^b = b log a, we have
 Or 3x log 5 = (x+4) log 3,
 Remove x log 3 to the left hand side and factor out x:
 (3 log 5 - log 3)x = 4 log 3,
 Or (log 5^3 - log 3)x = 4 log 3,
 Or (log 125 - log 3)x = 4 log 3,
 Or (log 125/3)x = 4 log 3,

 So, x = 4 log 3/log (125/3)

 If we convert it to log of base 3,we have
 x = 4 log3 3/log3 (125/3)
   = 4 / (log3 125 -1)