Срочно пожалуйста))очень надозаранее спасибо

$\frac{x}{13} = 51 \\ x = 51 \times 13 \\ x = 663$
7.
$\frac{10}{11} - \frac{4}{11} + \frac{3}{11} = \frac{10 - 4 + 3}{11} = \frac{9}{11}$
$4 \ \frac{5}{9} + 3 \ \frac{8}{9} = 7 \ \frac{13}{9} = 8 \ \frac{4}{9}$
$6 - 2\frac{2}{3} = 5\frac{3}{3} - 2 \ \frac{2}{3} = 3 \frac{1}{3}$
$5 \frac{6}{13} - 1 \frac{11}{13} = 4 \frac{13}{13 } + \frac{6}{13} - 1 \frac{11}{13} = 4 \frac{19}{13} - 1 \frac{11}{13} = 3 \frac{8}{13}$
8.
$5 \frac{6}{7} - x = 3 \frac{2}{7} \\ - x = 3 \frac{2}{7} - 5 \frac{6}{7} \\ - x = - (5 \frac{6}{7} - 3 \frac{2}{7} ) \\ - x = - 2 \\ x = 2$