what's the mean of 324g 569g 280g 300g 146g 63g 92g 451g

Basically, you would, like CPhill said, add the values. 324+569+280+300+146+63+92+451 is 2225, and dividing that by the number of values (8) would get a final answer of the mean being 278.125, also translated as 278 1/8.

Just add the values and divide by the number of them, i.e.,  8.