What is the mass? Calculus physical applications

If a 3 meter cylindrical bar has a constant density of p=3 g/cm for its left half and a constant density p=4 g/cm for its right half, what is mass?

The left side is 1.5 meters (150 cm) long and weighs 3g/cm. Therefore it weighs 450 g.
The right side is 1.5 meters (150 cm) long and weighs 4g/cm. Therefore it weighs 600 g.

Together the two halves weigh 1050 g or 1.05 kg.

Hope this helps.