Answer :
[tex]6+\frac{4}{5}b=\frac{9}{10}b\ \ \ \ \ \ |multiply\ both\ sides\ by\ 10\\\\60+2\times4b=9b\\\\60+8b=9b\ \ \ \ \ \ |subtract\ 60\ from\ both\ sides\\\\8b=9b-60\ \ \ \ \ \ |subtract 9b\ from\ both\ sides\\\\-b=60\\\\\boxed{b=-60}[/tex]