15.59 Independent random samples of the selling prices of same size spatula for four different materials were taken. The selling prices are shown in the following table. Test the null hypothesis that population mean selling prices are the same for four different materials.

Silicone Wood Rubber Metal 17 20 11 32 39 17 4 64 10 12 6 62 11 10 15 21 38 28 3 33 28 9 15 62