C) {5x - 3y = 14                                                    

    {X + 2y = -5

- 5x + 3y = -14

5x + 10y = -25

13y= -39

y= -39/13

y=-3

5x -3y= 14

5x-3.(-3)=14

5x+9=14

5x= 14-9

5x= 5

x= 5/5

x= 1

S= {(1,-3)}

C) {2x-3y=4

    {4x+2y=-8

{-8x+12y=-16

{8x+4y=-16

16y=-32

y=-32/16

y=-2

2x-3y=4

2x-3.(-2)=4

2x+6=4

2x=4-6

2x=-2

x=-2/2

x=-1

S={( -1,-2 )}

Espero ter ajudado