The accompanying table below shows how total donations, average donations, total labor costs and average labor costs vary depending on the number of employees State U hires for its fundraising activities. 
The marginal cost of the 4ᵗʰ employee is:
Definitions:
Motion Parallax
A depth cue in visual perception where objects closer to the viewer move faster across the visual field than objects further away.
Binocular Disparity
The difference in the visual images on the retinae of the two eyes that provides an important cue for depth perception.
Linear Perspective
A depth cue that parallel lines appear to converge in the distance and objects appear smaller as their distance from the observer increases, contributing to the perception of depth.
Apparent Convergence
The perception of two parallel lines appearing to come together at a distance.
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Q44: The extra benefit that results from carrying
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Q130: Larry was accepted at three different graduate
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Q140: If a linear, two-good production possibilities curve