a, x : $\frac{3}{4}$ + $\frac{1}{4}$ = $\frac{2}{3}$
x : $\frac{3}{4}$ = $\frac{2}{3}$ - $\frac{1}{4}$
x : $\frac{3}{4}$ = $\frac{5}{12}$
x = $\frac{5}{12}$ . $\frac{3}{4}$
x = $\frac{5}{16}$
b, $\frac{3}{4}$ . x + $\frac{1}{5}$ = $\frac{1}{3}$
$\frac{3}{4}$ . x = $\frac{1}{3}$ - $\frac{1}{5}$
$\frac{3}{4}$ . x = $\frac{2}{15}$
x = $\frac{2}{15}$ : $\frac{3}{4}$
x = $\frac{8}{45}$
c, 16[($\frac{3}{5}$ . x + 8):21 + 9] = $\frac{7}{10}$
($\frac{3}{5}$ . x + 8):21 + 9 = $\frac{7}{10}$ : 16
($\frac{3}{5}$ . x + 8):21 + 9 = $\frac{7}{160}$
($\frac{3}{5}$ . x + 8):21 = $\frac{7}{160}$ - 9
($\frac{3}{5}$ . x + 8):21 = $\frac{-1433}{160}$
$\frac{3}{5}$ . x + 8 = $\frac{-1433}{160}$ x 21
$\frac{3}{5}$ . x + 8 = $\frac{-30093}{160}$
$\frac{3}{5}$ . x = $\frac{-30093}{160}$ - 8
$\frac{3}{5}$ . x = $\frac{-31373}{160}$
=> x = $\frac{-31373}{96}$
