Simplify the expression x3/8y3x7/8y3/4x7/16y4\displaystyle \frac{{{x}^{{{3}/{8}}}{y}^{{{3}}}{x}^{{{7}/{8}}}{y}^{{{3}/{4}}}}}{{{x}^{{{7}/{16}}}{y}^{{{4}}}}}. Write your answer in rational exponent form,using nonnegative exponents.