[tex](6 \frac{2}{5} + 4 \frac{7}{15} ) + (6 \frac{2}{5} - 4 \frac{7}{15} ) = (6 \frac{6}{15} + 4 \frac{7}{15} ) + (6 \frac{6}{15} - 4 \frac{7}{15} ) = 10 \frac{13}{15} + (5 \frac{21}{15} - 4 \frac{7}{15} ) = 10 \frac{13}{15} + 1 \frac{14}{15} = 11 \frac{27}{15} = 12 \frac{12}{15} [/tex]
