Answer:
Widgets should be sold by $38.88 to maximize the profit.
Step-by-step explanation:
Vertex of a quadratic function:
Suppose we have a quadratic function in the following format:

It's vertex is the point 
In which


Where

If a<0, the vertex is a maximum point, that is, the maximum value happens at
, and it's value is
.
In this question:
The profit is given by:

Which is a quadratic function with 
The maximum profit happens at the x of the vertex. Thus

Widgets should be sold by $38.88 to maximize the profit.
It is given in the question that
Ann, Chang, and Kareem sent a total of 89 text messages over their cell phones during the weekend. Ann sent 9 fewer messages than Chang. Kareem sent 3 times as many messages as Ann.
Let number of messages Chang sent be x. And Ann sent 9 fewer than Chang, so Ann sent (x-9) messages. And Kareem sent 3 times as many messages as Ann, so Kareem sent 3(x-9) messages.
And the total messages are 89. That is

Combining like terms

So Chang sent 25 messages, Ann sent

And Kareem sent

3/4 times 5=
5 times 3=15
15/4=3 3/4
3 3/4 is answer
The area for a circle with a diameter of 8 cm is 50.24 cm². The area of a circle with a radius of 3 cm is 28.26 cm². 50.24 - 28.26 = 21.98 cm. So the difference is 21.98 cm.