3 percent = 0.03

0.03x =

$120 - $100 - $14 = $6

$20 is 20% of $100
$6 is 6% of $100
percent difference is 14%. $14 = 14%


$1200 - $1000 - $14 = $186

$200 is 20% of $1000
$186 is 18.6% of $1000
percent difference is 1.4%. $14 = 1.4%

I want to make at least $28. I want to make at least as much on each trade
as TDAmeritrade is making from me.
$142 - 100 - $14 = $28. 42% change
(.42x + x) - x - $14 = $28
(xy + x) - x - $14 = $28
where x is the amount invested and y is the percentage gained
how big does x have to be for y to be 1?
.01x + x - x - 14 = 28
1.01x - x - 14 = 28
.01x - 14 = 28
.01x = 42
x = $4200