Density is mass per unit of volume which pair of lab instruments would a student use to measure the density of seawater?

Aprimary producer stores 9,000 kcal. in the energy pyramid, if a primary producer is consumed by a first-level consumer, and that first-level consumer is consumed by a second-level consumer and the second-level consumer is consumed by a third-level consumer, how much energy is stored by the third-level consumer from the primary producer? *