[tex]2 \frac{1}{4} - ( - 4 \frac{1}{5} ) = 2 \frac{1}{4} + 4 \frac{1}{5} = \\ 2 \frac{5}{20} + 4 \frac{4}{20} = 6 \frac{9}{20} = 6.45[/tex]