algebra

Depends on what G and b are!

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G and b must be a value and this is an example to you  $${\mathtt{G}}{\mathtt{\,-\,}}{\mathtt{b}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}} = {\mathtt{5}} \Rightarrow {\mathtt{g}} = {\mathtt{b}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2}}$$