24 !
a solid is warmed. assuming the mass remains constant, how, if at all, does this effect the density of the solid?

The pressure in the solid is released from heat or if you want to get more technical
"Density (D) is equal to mass (m) divided by volume (V). So: if D = m/V, when V increases, D will decrease if m is constant. The general meaning of density is the amount of anything per unit volume. What we conventionally call the "density" is more precisely known as the "mass density". However, one can also construct other densities like a "charge density" for example.

Density can be expressed in any combination of mass and volume units; the most commonly seen units are grams per mL (g mL–1, g cm–3), or kilograms per liter" 

The answer is constant.