Answer:
The measurement of the central angle AOB is 45 degrees
Step-by-step explanation:
To solve this problem, we will have to work with fractions.
We will get the fraction of area the shaded portion is when compared to the whole garden.
First of all, we will need to calculate the area of the garden which is 
in this case, our radius is 8 inches.
Next, we will compare the area of the sector to the area of the garden. This will be
This will be the shaded area/ area of the whole garden
= 

We will now convert this ratio to an angle by multiplying it by 360 degrees.
This will be:

The measurement of the central angle AOB is 45 degrees
<span>30x + 30y = 450 20x + 25y = 345
Here 345 represents the total area (in sq ft) shoveled; x repres. Melinda's rate and y represents Paul's rate. We need to solve for x and y and then subtract the smaller from the larger.
</span>30x + 30y = 450 Multiply this eqn by 2: 6<span>0x + 60y = 900
</span>20x + 25y = 345 Mult this eqn by -3: -60x -75y = -1035
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-15y = -135
y = 9
This comes to 9 square feet per minute.
Now, let's find x: 30x + 30y = 450; 30x + 270 = 450; 30x = 180; x = 6
Melinda can shovel 6 sq ft in 1 min, whereas Paul can shovel 9.
The difference is (9 - 6) sq ft / min, or 3 sq ft / min (answer)
1 hour = 60 minutes
60/3 is 20 minutes
20/4 is 5 minutes
Samantha spends 5 minutes on each chore