Suspended from a spring balance is a 20 N metal block. A beaker...

Initial reading of the spring balance is $20 \text{ N}$ and the final reading is $16 \text{ N}$.

The loss in weight of the block is equal to the buoyant force exerted by the water.

Buoyant force $F_B = 20 \text{ N} - 16 \text{ N} = 4 \text{ N}$.

According to Newton's third law, the block exerts an equal and opposite downward force of $4 \text{ N}$ on the water.

The total downward force on the weighing machine increases by the magnitude of this reaction force.

New reading on the weighing machine = $40 \text{ N} + 4 \text{ N} = 44 \text{ N}$.