Given that the rational numbers a and B are not zero, and a + = 3B = 0, find the value of the third power of a minus B

Given that the rational numbers a and B are not zero, and a + = 3B = 0, find the value of the third power of a minus B

a+3b=0,a=-3b,a/-b=3
The third power of a is 27
a+=3b=0,a=3b,a/-b=-3
The third power of a minus B = - 27