Why does Alex’s equation better represent the reaction?

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Indicate whether the specified alkyl halides will form primarily substitution products, only elimination products, both substitution and elimination products, or no products when they react with sodium methoxide. 1-bromobutane 1-bromo-2-methylpropane 2-bromobutane 2-bromo-2-methylpropane

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