A) 4x+2y =7
2y= 7 -4x
y = 7/2 -2x
y = -2x +3,5
4x=7-2y
x = 7/4 -y/2
x= - y/2 + 1,75
б) -5x+y = -12
y = 5x-12
5x= y+12
x= y/5 + 2,4
в)
x+15y = -30
15y = - x - 30
y= -x/15 -2
x= -15y -30
г) 3y-14x =21
3y = 14x +21
y = 14x/3 +21/3
y = 4 2/3 *x +7
14x=3y-21
x = 3y/14 -21/14
x =3y/14 - 1,5