А)(21m-19)-(1+4m)=12m, 21m - 19 - 1 - 4m =12m
21m - 4m - 12m = 19 + 1
5m = 20
m= 20:5
m = 4
б)(32-7n)+(64+17n)=19-(6n-13),
32 - 7n +64 +17n =19 - 6n +13,
-7n + 17n +6n = 19 + 13 - 32 - 64,
16n = -64
n = (- 64):16
n = - 4
в)2,4х-(х-4,2)= -6,3+(0,4х+3,3)
2,4x - x + 4,2 = -6,3 +0,4x +3,3,
2,4x -x -0,4x=- 6,3+3,3-4,2
x = -7,2