4) 12 - 6 + 4 - 1

1. Convert mixed numbers to improper fractions: $$12\frac{3}{20} = \frac{243}{20}$$, $$6\frac{7}{8} = \frac{55}{8}$$, $$4\frac{1}{2} = \frac{9}{2}$$.
2. Find a common denominator (40): $$\frac{243}{20} = \frac{486}{40}$$, $$\frac{55}{8} = \frac{275}{40}$$, $$\frac{9}{2} = \frac{180}{40}$$.
3. Perform the operations: $$\frac{486}{40} - \frac{275}{40} + \frac{180}{40} = \frac{211}{40} + \frac{180}{40} = \frac{391}{40} = 9\frac{31}{40}$$.