Answer:
<em>M(13)=14.3 gram</em>
Step-by-step explanation:
<u>Exponential Decay Function</u>
The exponential function is used to model natural decaying processes, where the change is proportional to the actual quantity.
An exponential decaying function is expressed as:

Where:
C(t) is the actual value of the function at time t
Co is the initial value of C at t=0
r is the decaying rate, expressed in decimal
The element has an initial mass of Mo=970 grams, the decaying rate is r=27.7% = 0.277 per minute.
The equation of the model is:


Operating:

After t=13 minutes the remaining mass is:

Calculating:
M(13)=14.3 gram
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Answer:
The answer is (C)
The equation of the circle is (x + 4)² + (y - 6)² = 81
Step-by-step explanation:
* To find the equation of the circle you need to know
the center of the circle and the length of its radius
* The rule of the equation of the circle is:
(x - h)² + (y - k)² = r²
Where x and y is a general point on the circle,
h and k are the coordinates of the center of the circle
and r is the radius of the circle
∵ The center of the circle is (-4 , 6)
∵ The radius of the circle is 9
∴ (x - -4)² + (y - 6)² = 9²
∴ ( x + 4)² + (y - 6)² = 81
∴ The answer is (C)