My Ti-89 got $${\mathtt{\,-\,}}\left({\mathtt{6}}{\mathtt{\,\times\,}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{b}}{\mathtt{\,-\,}}{\mathtt{7}}\right)}^{{\mathtt{2}}}\right)$$. I am not sure why we are getting different answers.
Last time I did calculus was in 2009.
But here is a complete work through and a calculator you can use on line, which gave the same as my TI-89
https://www.symbolab.com/solver/derivative-calculator/%5Cfrac%7Bd%7D%7Bdb%7D%5Cleft(%5Cleft(7-2b%5Cright)%5E%7B3%7D%5Cright)/?origin=button
