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14. a) $\frac{7}{5}$ + $\frac{21x}{35}$ = x    x- $\frac{21x}{35}$ = $\frac{7}{5}$     aducem la acelasi numitor 35

35x-21x= 35     14 x= 35   x= 35/14= $\frac{5*7}{2*7}$= $\frac{5}{2}$   x= $\frac{5}{2}$

b) $\frac{10}{3}$ - $\frac{5x}{15}$ = x       x+ $\frac{5x}{15}$ = $\frac{10}{3}$      15x+5x= 5*10

20x= 50   => x= 50:20 =5/2  x= 5/2

c) $\frac{9}{7}$ - $\frac{15x}{21}$ = x     x+ $\frac{15x}{21}$ = $\frac{9}{7}$     21x+15x= 9*3

36x= 9*3=>  x= 9*3: 4*9= 3/4  x= 3/4

d) $\frac{18}{7}$ + $\frac{99x}{63}$ = x        x-  $\frac{99x}{63}$ = $\frac{18}{7}$      63x-99x= 18*9

-36x= 2*81  => x= - 2*81:36= - 9/2   x=-9/2

15.a)  $\frac{5}{2}$ *$\frac{6x}{9}$   - $\frac{5}{2} * \frac{4}{10}$ = x       $\frac{15x}{9} -1= x$        15x-9x= 1*9

6x=9   => x= 9/6     x= 3/2

b) $\frac{12}{10}$ * $\frac{3x}{9}$ + $\frac{12}{10} * \frac{75}{100}$ =x     x- $\frac{4x}{10}$ = $\frac{9}{10}$     10x- 4x= 9  

6x=9   x= 9/6    x= 3/2

c) $\frac{4}{10} * \frac{15x}{9}$  + $\frac{4}{10} * \frac{5}{4}$ = x        x- $\frac{2x}{3}$ = $\frac{1}{2}$        6x-4x= 3

2x=3   => x=3/2

d) $\frac{25}{10} * \frac{12x}{90}$  - $\frac{25}{10} * \frac{16}{100}$ = x       x- $\frac{x}{3}$ = $\frac{2}{5}$      15x-5x= 6

10x=6   x= 6/10 = 3/5   x= 3/5

16. a) $\frac{5}{4} - \frac{1}{4} * \frac{1}{6x}$ = $\frac{6}{5}$    $\frac{5}{4}$ - $\frac{6}{5}$  = $\frac{1}{24x}$       $\frac{5*5-6*4}{20}$= $\frac{1}{24x}$      $\frac{1}{20}$= $\frac{1}{24x}$=>

24x= 20   => x= 20/24= 5/6    x=5/6

b) $\frac{6}{5}$ + $\frac{2}{5}* \frac{1}{4x}$ = $\frac{4}{3}$         $\frac{4}{3} - \frac{6}{5}$ = $\frac{1}{10x}$     $\frac{20-18}{15}$ = $\frac{1}{10x}$       $\frac{2}{15}$= $\frac{1}{10x}$=>

2*10x= 15*1   /:5   4x= 3  => x= 3/4  

c) $\frac{1}{3} * \frac{1}{5x}$ - $\frac{1}{3} * 7$ = $-\frac{5}{2}$       $\frac{1}{15x}$ = $\frac{7}{3} -\frac{5}{2}$      $\frac{1}{15x}$ = $\frac{14-15}{6}$  = - $\frac{1}{6}$

15x=-6   => x= -6/15 = -2/5    x= -2/5