Elementary Algebra

$\dfrac{5y}{7}$
Cancelling the common factor between the numerator and the denominator, the given expression, $\dfrac{55xy}{77x} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{\cancel{11x}\cdot5y}{\cancel{11x}\cdot7} \\\\= \dfrac{5y}{7} \end{array}