资料：Elizabeth Blackwell was born in England in 1821, and moved to New York City when she was ten years old. One day she decided that she wanted to become a doctor. That was nearly impossible for a woman in the middle of the nineteenth century.After writing many letters asking for admission (录取) to medical schools, she was finally accepted by a doctor in Philadelphia. She was so determined that she taught school and gave music lessons to get money for the cost of schooling.

In 1849, after graduation from medical school, she decided to further her education in Paris. She wanted to be a surgeon (外科医生) , but a serious eye problem forced he r to give up the idea.

Upon returning to the United States, she found it difficult to start her own practice because she was a woman. By 1857 Elizabeth and her sister, also a doctor, along with another woman doctor, managed to open a new hospital, the first for women and children Besides being the first woman physician and founding her won hospital, she also set up the first medical school for women.

How many years passed between her graduation from medical school and the opening of her hospital?