Chapter 12 - Vectors and the Geometry of Space - 12.5 Equations of Lines and Planes - 12.5 Exercises - Page 873: 73

$\frac{5}{2\sqrt {14}}$

Distance formula between two parallel planes is given as: $D=\frac{|ax+by+cz+d|}{\sqrt {a^2+b^2+c^2}}$ $D=\frac{|0+0+2 \times 4-3|}{\sqrt {4^2+6^2+2^2}}=\frac{5}{\sqrt {56}}$ $=\frac{5\sqrt {14}}{28}$ $=\frac{5}{2\sqrt {14}}$