Chapter 7 - Section 7.2 - Rational Exponents - Exercise Set - Page 425: 64

$3x^{3/2}+3x^{1/2}y$

Using the Distributive Property and the laws of exponents, then, \begin{array}{l} 3x^{1/2}(x+y) \\\\= 3x^{\frac{1}{2}+1}+3x^{1/2}y \\\\= 3x^{\frac{1}{2}+\frac{2}{2}}+3x^{1/2}y \\\\= 3x^{3/2}+3x^{1/2}y .\end{array}