7 3/8 -1 1/4 = ?
$$7 \frac{3}{8} -1 \frac{1}{4}\\\\
=7 + \frac{3}{8} -1 - \frac{1}{4}\\\\
=7 -1 + \frac{3}{8} - \frac{1}{4}\\\\
=6 + \frac{3}{8} - \frac{1}{4}\\\\
=6 + \frac{3}{8} - \frac{1*2}{4*2}\\\\
=6 + \frac{3}{8} - \frac{2}{8}\\\\
=6 + \frac{1}{8}\\\\
=6\frac{1}{8}$$