Реши уравнение: a-9/16*a=5 1/4.

\[a - \frac{9}{16}a = 5\frac{1}{4}\]

\[a\left( 1 - \frac{9}{16} \right) = 5\frac{1}{4}\]

\[a\left( \frac{16}{16} - \frac{9}{16} \right) = 5\frac{1}{4}\]

\[\frac{7}{16}a = \frac{21}{4}\]

\[a = \frac{21}{4}\ :\frac{7}{16} = \frac{21}{4} \cdot \frac{16}{7}\]

\[a = \frac{3 \cdot 7 \cdot 4 \cdot 4}{4 \cdot 7}\]

\[a = 12\]

\[Ответ:\ a = 12.\]