well the other persons answer is confusing because its all separated so here:
Rewrite 
log(2x)=4
log2x=4 in exponential form using the definition of a logarithm. If 
x
x and 
b
b are positive real numbers and 
b
b
≠
≠
1
1, then 
log
b(x)=y
logbx=y is equivalent to 
by=x
by=x.
10
4
=
2x