\[\boxed{\mathbf{3.84}}\]
Пояснение.
Решение.
\[\textbf{а)}\ 7\ :28 = 5,5\ :4x\]
\[4x = \frac{28 \cdot 5,5}{7}\]
\[x = \frac{4 \cdot 5,5}{4}\]
\[x = 5,5.\]
\[\textbf{б)}\ 3x\ :11 = 1\frac{1}{2}\ :2\frac{3}{4}\]
\[3x \cdot 2\frac{3}{4} = 11 \cdot 1\frac{1}{2}\]
\[3x = 11 \cdot \frac{3}{2}\ :\frac{11}{4}\]
\[3x = 11 \cdot \frac{3}{2} \cdot \frac{4}{11}\]
\[3x = 6\]
\[x = 6\ :3\]
\[x = 2.\]
\[\textbf{в)}\ 1,35\ :0,6 = 1,08\ :0,4x\]
\[1,35 \cdot 0,4x = 1,08 \cdot 0,6\]
\[x = \frac{108 \cdot 6}{135 \cdot 4} = \frac{27 \cdot 2}{45} = \frac{3 \cdot 2}{5}\]
\[x = 1,2.\]
\[\textbf{г)}\ 2\frac{1}{4}\ :1 = 3x\ :\frac{2}{3}\]
\[3x = 2\frac{1}{4} \cdot \frac{2}{3}\]
\[3x = \frac{9}{4} \cdot \frac{2}{3} = \frac{3}{2}\]
\[3x = 1,5\]
\[x = 1,5\ :3\]
\[x = 0,5.\]