Percent copper in this copper-zinc alloy?

I'm just..confused...

The density of a material made up of two or more different substances will be a weighted average of the substances that make it up. (what is a weighted average?) Suppose you have a block of copper-zinc alloy that has a density of 7.76 g/cm^3. Calculate the percent copper in the alloy. (density of copper = 8.92 g/cm^3 ; density of zinc = 7.16 g/cm^3)

I'm just not sure what to do. Since copper is more dense than zinc, I'm assuming that there is more copper in this alloy than zinc, I just don't know how to calculate the exact percentage.

Any pointers are appreciated! Thanks!