David's age: x
Joshua: x + 5
Simon: (x+5) + 4 or x + 9
Simon's age + David's age = 15
(x+9) + (x) = 15
2x = 15 - 9
2x/2 = 6/2
x = 3
The ages of the boys:
David: x = 3 years old
Joshua: 3+5 = 8 years old
Simon: 3+9 = 12 years old
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Answer:
Step-by-step explanation:
A. Function before discount:
f(c)= 8.97c
This means that cost per strand of outdoor light is $8.97 and c is number of strands of outdoor light bought. Therefore to model the function g(c) after he has received a $5 discount on his purchase(total purchase)
g(c)=8.97c-5
B. cost of 6 strands of light before discount
f(c)= 8.97×6= $53.82
cost of 6 strands of light after discount
f(c)=8.97×6-5= $48.82
Given:


To find:
The rate of change in volume at 
Solution:
We know that, volume of a cone is

Differentiate with respect to t.
![\dfrac{dV}{dt}=\dfrac{1}{3}\pi\times \left[(r^2\dfrac{dh}{dt}) + h(2r\dfrac{dr}{dt})\right]](https://tex.z-dn.net/?f=%5Cdfrac%7BdV%7D%7Bdt%7D%3D%5Cdfrac%7B1%7D%7B3%7D%5Cpi%5Ctimes%20%5Cleft%5B%28r%5E2%5Cdfrac%7Bdh%7D%7Bdt%7D%29%20%2B%20h%282r%5Cdfrac%7Bdr%7D%7Bdt%7D%29%5Cright%5D)
Substitute the given values.
![\dfrac{dV}{dt}=\dfrac{1}{3}\times \dfrac{22}{7}\times \left[(120)^2(-2.1) +175(2)(120)(1.4)\right]](https://tex.z-dn.net/?f=%5Cdfrac%7BdV%7D%7Bdt%7D%3D%5Cdfrac%7B1%7D%7B3%7D%5Ctimes%20%5Cdfrac%7B22%7D%7B7%7D%5Ctimes%20%5Cleft%5B%28120%29%5E2%28-2.1%29%20%2B175%282%29%28120%29%281.4%29%5Cright%5D)
![\dfrac{dV}{dt}=\dfrac{22}{21}\times \left[-30240+58800\right]](https://tex.z-dn.net/?f=%5Cdfrac%7BdV%7D%7Bdt%7D%3D%5Cdfrac%7B22%7D%7B21%7D%5Ctimes%20%5Cleft%5B-30240%2B58800%5Cright%5D)


Therefore, the volume of decreased by 29920 cubic inches per second.
To find the answer to this, you have multiply both expressions by each other. To do this, you have to multiply each term in the first expression by each term in the second expressions. This yields the following: 3x^4-9x^3-3x^2+5x^3-15x^2-5x+10x^2-30x-10. Combing like terms and simplifying gives the final expression: 3x^4 - 4x^3 - 8x^2 - 35x - 10