In each case, determine whether the given ratios are equivalent.
\dfrac{4}{9} and \dfrac{9}{38}
\dfrac {2} {3} and \dfrac{9}{12}
\dfrac{3}{9} and \dfrac{2}{6}
\dfrac {12} {27} and \dfrac {8} {18}
\dfrac {5} {12} and \dfrac {7} {13}
\dfrac {25} {45} and \dfrac {5} {9}
\dfrac {15} {105} and \dfrac {3} {21}