Law of Exponent
[tex] \displaystyle \large{( \frac{a}{b} )^{n} = \frac{ {a}^{n} }{ {b}^{n} } }[/tex]
From the expression.
[tex] \displaystyle \large{( \frac{2}{3} )^{2} = \frac{ {2}^{2} }{ {3}^{2} } = \boxed{\frac{4}{9} } }[/tex]
Jerome's mistake is that Jerome forgot to evaluate 2^2 or forgot to add 2^2. The denominator is correct but the numerator is wrong.