Answer:
3×81^x=9^{x+4}
since power of no is multiplied to its remaining power
3×3^4x=3^2{x+4}
if there is like terms then power is added
3^{1+4x}=3^{2x+8}
if there is like terms then power can be compared
so{1+4x}={2x+8}
1+4x=2x+8
4x-2x=8-1
2x=7
x=7/2 is your answer
