Ответ:
1.
x=5-y
3(5-y)-2y = 3
15-3y-2y = 3
-5y = -12
y = 12/5 = 2,4
x = 5-2,4 = 2,6 = 13/5
2.
карандаш - х
ручка - у
4x+3y = 70
2x+y = 28
y = 28-2x
4x+3(28-2x) = 70
4x+84-6x = 70
-2x = -14
x = 7
y = 28-2*7 = 14
3.
11x+8y+5x-16y = 27+(-27)
16x-8y = 0
8(2x-y) = 0
2x-y = 0
y = 2x
11x+16x = 27
27x = 27
x = 1
y = 2
4.
подставляем координаты в уравнение прямой:
k+b = -2
-3k-b = -10
k = -2-b
-3(-2-b)-b = -10
6+3b-b = -10
2b = -16
b = -8
k = 6
уравнение: y=6x-8
5.
b = -3+3a
3a+3-3a = 3
0=0
x є R
количество решений неограничено
6.
4a-2b = 5
4a-6 = 7-b
4a = 5+2b
a = 5+2b/4
4(5+2b)/4 - 6 - 7 + b = 0
5+2b-13+b = 0
3b = 8
b = 8/3
a = 31/12