\[\boxed{\mathbf{465}.}\]
\[1)\ 0,9x = 0,54\]
\[x = 0,54\ :0,9\]
\[x = 5,4\ :9\]
\[x = 0,6.\]
\[2)\ 9,2y = 3,68\]
\[y = 3,68\ :9,2\]
\[y = 36,8\ :92\]
\[y = 0,4.\]
\[3)\ 42,21\ :x = 4,2\]
\[x = 42,21\ :4,2\]
\[x = 4221\ :420\]
\[x = 10,05.\]