` \frac{(5^{4}-5^{3})^3}{125^4} `
` = \frac{(5^{4}-5^{3})^3}{125^{3}.125} `
` = \frac{(5^{4}-5^{3})^3}{125^{3}.5^{3}} `
` = \frac{(5^{4}-5^{3})^3}{(125.5)^{3}} `
` = (\frac{5^4 - 5^3}{125.5})^3 `
` = (\frac{5.(5^3 - 5^2)}{125.5})^3`
` = (\frac{5^3 - 5^2}{125})^3 `
` = (\frac{125 - 25}{125})^3 `
` = (100/125)^3 `
` = (4/5)^3 `
` = 64/125 `