The exponent ^2/3 means ^(1/3)*2 which means the cube root squared. The contents of the brackets contains exponents divisible by 3: cube root of x^3 is x and cube root of y^-6 is y^-2. The cube root of -8 is -2 and the cube root of 1 is 1 so we can work out the contents of the brackets after taking the cube root of everything in them: -2x/y^-2. 1/y^-2 is y^2 which comes from 1/(1/y^2); we simply invert the fraction 1/y^2=y^2. So now we have -2xy^2. Only one more thing to do. We have to square this because the exponent outside the brackets is 2/3 and the 2 says "square the cube root" so we square -2xy^2 giving 4x^2y^4 and minus sign turns to plus: -2 times -2 is 4; x becomes x^2 and y^2 becomes y^4.