The third one is the answer for this question
Step-by-step explanation:
This is a linear equation in slope intercept form which is

where m is the slope and b is the y intercept.
The equation

Has a slope of -1/3 so this means that the slope will be decreasing. A negative linear equation increases as we go left. and decreases as we go right. The y intercept is 2. So this means the graph must pass through (0,2) and when x=0, y must be 2.
In other words, look for a line that the y values increase as we go left and decrease we go right. Also look for a point (0,2) and make sure the graph pass through it.
You do Y2-Y1 Divided by X2-X1
The statement "unit cubes with side lengths of 1/2 foot are added to fill the prism with no space remaining" is useless information so you can disregard that. All you need to know to calculate the volume is the length, width, and height.
Volume = length x width x height
Volume = (5/2) x 3 x 11/2
Volume = 15/2 x 11/2
Volume = 165/4
Volume = 41.25 ft cubed