Решение, при -6/2/3 = -2/3, а не -6/(2/3) = -9:
1) -6/2/3 * -1/1/5 - 1/2 + x = 0
-3/3 * -1/5 - 1/2 = -x
2(-1 * -1/5 - 1/2) = -x*2
2/5 - 1 = -2x
(-5+2)/5 = -2x
-3/5 = -2x
x = 3/10
x = 0.3
2) (-5*21)/(14*25) - 3/3/4 = y
(-1*21)/(14*5) - 3/3/4 = y
(-1*3)/(2*5) - 3/3/4 = y
-3/10 - 1/4 = y
((-3*4) - (1*10)) / 40 = y
(-12 - 10)/40 = y
y = -22/40
y = -11/20