I would say 25 is the answer to it
The tree is 7.5ft because it's shadow is half it's height.
Answer:

Step-by-step explanation:
Given that,
Mass of material, m = 6900 grams
Volume of the material, V = 4.5 quarts
We need to find the density in pounds per cubic foot
We know that,
1 pound = 453.59 grams
⇒ 6900 grams = 15.21 pounds
Also, 1 cubic foot = 29.92 quarts
4.5 quart = 0.15 feet³
Density = mass/volume
Or

Hence, the density of the material is 
Michael worked 4.5 hours. 65.75 - 36.50 = 29.25, therefore, Michael made $29.25 not including tips. 29.25/6.50 = 4.5