Resposta :
1)Livro= x
Caderno= y
a) 2x + 5y = 150
2)16-11x+12=-15
-11x = -15 -16 -12
-11x = -43.(-1)
+11x = +43
x= 43/11
3)60+13x=3x
13x -3x = -60
10x= -60
x= -60/10
x= -6
Caderno= y
a) 2x + 5y = 150
2)16-11x+12=-15
-11x = -15 -16 -12
-11x = -43.(-1)
+11x = +43
x= 43/11
3)60+13x=3x
13x -3x = -60
10x= -60
x= -60/10
x= -6