Question 131555
You are misinterpreting the {{{E[o]}}} and the {{{E[i]}}}
The little "o" and "i" are not bases, they are called
subscripts. All a subscript does is give you a way to 
narrow the definition of a variable.
Example:
Suppose {{{R}}} is the rent I charge for apartments
Maybe I use {{{R}}} in a formula, but I want to know
if the rent is for a 1-bedroom, 2-bedroom, or 3-bedroom
{{{R[1]}}}= rent is for a 1-bedroom
{{{R[2]}}}= rent is for a 2-bedroom
{{{R[3]}}}= rent is for a 3-bedroom
Just realise that sometimes little numbers do refer to
the base for a log, just not in this case
{{{E[i] = .5}}} volts ({{{E[i]}}} is voltage in)
{{{E[o] = 52}}} volts ({{{E[o]}}} is voltage out)
{{{d = 10*log(10,(E[o]/E[i]))}}}
{{{d = 10*log(10,(52/.5))}}}
{{{d = 10*log(10,104)}}}
{{{d = 10*2.017}}}
{{{d = 20.17}}} answer