It's still context-free, the reason is because by the time you hit the '=' symbol you already know whether you're in a <Statement> or a <Compare Exp> production

It's still context-free, the reason is because by the time you hit the '=' symbol you already know whether you're in a <Statement> or a <Compare Exp> production rule, based on the preceding symbols (namely the LET keyword), based on these excerpts from the BASIC EBNF: <Statement> ::= CLOSE '#' Integer | DATA <Constant List> [...] | LET Id '=' <Expression> [...] | Remark <Compare Exp> ::= <Add Exp> '=' <Compare Exp> | <Add Exp> '<>' <Compare Exp> | <Add Exp> '><' <Compare Exp> | <Add Exp> '>' <Compare Exp> | <Add Exp> '>=' <Compare Exp> | <Add Exp> '<' <Compare Exp> | <Add Exp> '<=' <Compare Exp> | <Add Exp>