a/-285 + (-28) + 285 + 12
= -285 + 285 + (-28) + 12
= 0 + (-16)
= -16
b/24 : {390 : [500 - (160 + 210 )]}
=24 : {390 : [500 - 370]}
=24: {390 : 130}
=24 : 3
=8
2/
a/ x - 5.3 mũ 2 = 18 : 3 mũ 2
x - 5.9 = 18 : 9
x - 5.9 = 2
x - 45 = 2
x = 2.45
x=90
b/100 - 5. (4x - 9 ) = 25
5. (4x - 9) = 100 - 25
5. (4x - 9) = 75
4x - 9 = 75 : 5
4x - 9 = 15
4x = 15+9
4x = 24
x = 24 :4
x = 6