Let's break down this problem step-by-step. It seems like there's some missing information in the second alloy description. I'll assume you meant to say "A second alloy contains 9 cm³ of copper and 11 cm³ of tin, and has a mass of 158 g."

Here's how to calculate the density of each alloy:

Understanding Density

Density is a measure of how much mass is packed into a given volume. It's calculated as:

Density = Mass / Volume

Alloy 1

* Volume = 8 cm³ (copper) + 7 cm³ (tin) = 15 cm³

* Mass = 121 g

* Density = 121 g / 15 cm³ = 8.07 g/cm³

Alloy 2

* Volume = 9 cm³ (copper) + 11 cm³ (tin) = 20 cm³

* Mass = 158 g

* Density = 158 g / 20 cm³ = 7.9 g/cm³

Therefore:

* The density of the first alloy is 8.07 g/cm³.

* The density of the second alloy is 7.9 g/cm³.