"A young girl wrote to ask, 'Why aren’t there any women on our currency?' And then she gave me like a long list of possible women to put on our dollar bills and quarters and stuff, which I thought was a pretty good idea," President Obama said during a recent speech.

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The young girl President Obama was talking about is Sofia.

A few years ago, when Sofia was 9 years old, she sent a letter to the White House with a list of suggestions of women she'd like to see on U.S. currency. One of those suggestions was Harriet Tubman.

"She came home from school one day and she said, 'Mom, I need to write to the president' so I gave her a piece of paper and that became the really famous letter," Sofia's mother, Kim, told ABC News. "She really is just a regular, average, little girl who noticed something that was unfair and decided to do something about it."

One of Sofia's reasons why women should be featured on currency? "If there were no women, there wouldn't be men," she wrote in her letter.

On Wednesday, Treasury Secretary Jack Lew called Sofia himself to share the news that her suggestion was heard and that Tubman will soon grace the $20 bill.

“Thank you for writing the president and thank you for writing to me and I thank you for helping to wake up the country,” Lew said.

It turns out the Treasury Department actually took two suggestions from Sofia’s list. Eleanor Roosevelt will appear on the back of the new $5 bill.

"Some kids think, ‘Well, I’m a kid. I can’t vote. Why should I be able to make a change at anything?' If you think of a way you can do something, even if you think it’s small, it can turn into something huge," Sofia said.