( CNN ) -- There 's a fine science to running a billion dollar company . Rosalind Brewer should know -- she used to study chemistry . Before she was CEO of American retail giant , Sam 's Club -- a company which boasted $ 56 billion in revenues last year -- Brewer earned a degree in science at Spelman College , Atlanta , Georgia . These days though , one of the first things she thinks about when she wakes up is her 107,000 employees . `` I owe them leadership , direction , and the chance to grow , '' says the chief of the retail warehouse chain , owned by Walmart . `` I take that as a personal responsibility . And I have to earn it every day . '' When 51-year-old Brewer took the job in 2012 , she became the first woman and the first African American to lead a Walmart division . Two years later , the number of Sam 's Club stores has grown from 610 to 643 across the U.S. and Puerto Rico . Could the 64th most powerful woman in the world , according to Forbes , one day have the top job at Walmart ? `` Oh boy , that is a good question , '' she says , laughing a little nervously . `` If ever I was afforded the opportunity , surely I would step up to the challenge . '' Here are four more insights from the former chemistry student . `` One of the best pieces of advice I 've received throughout my career was the importance of having honesty and integrity . It helped build me as a person and helped me stay consistent to my values . '' '' `` The first response from people is that I have a visible difference -- I 'm an African American female . I think they have this initial response which is 'What is she made of ? How did she get here ? ' '' `` Laying off 2,300 workers was very difficult . I take those moments really personally and we did a lot of work to make sure we were doing the right thing . '' `` What scares me ? Tornados . I think I can do a lot of things . But if that tornado is coming for me , I do n't think I can stop it . '' Rosalind is n't the only female science graduate aiming big . For the month of October , Leading Women celebrates women and girls in STEM : science , technology , engineering and mathematics . Join @ CNNIwomen 's Twitter chat with STEM experts on October 9 at 5pm GMT/12pm EST . # CNNWomen # IDG14 .
Meet Rosalind Brewer , the CEO of Sam 's Club , part of Walmart . Chemistry graduate now heads company worth billions of dollars . Comment: Laying off 2,300 workers was one of toughest moments of her life .