The fraction is 8^x / 2^y, Substitute y = 3x - 12 into fraction, 8^x / 2^[3x - 12] = 8^x / [(2^3)^x × 2^(-12)] = 8^x / [(2 × 2 × 2)^x × 2^(-12)] = 8^x / [8^x × 2^(-12)] {8^x can be factorised out of numerator and denominator of fraction} = 1 / 2^(-12) {When the denominator becomes numerator, the power sign is switched from - to +} = 2^(12)
