172 boys in class
we have total number of students in class = 410
we assume that the number of boys in class = X
Number of girls in class is 66 more then boyes we assume total number of girls = X+66
if we add number of girls and boyes then we found total strength of classX+X+66=4102X+66=4102x=344X=172
number of boys=172number of girls =238
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20859
We know that:

is an equation of a circle.
When we substitute x and y (from the pairs we have), we'll get a system of equations:

and all we have to do is solve it for a, b and r.
There will be:

From equations (II) and (III) we have:

and from (I) and (II):

Now we can easly calculate a and b:

Finally we calculate

:

And the equation of the circle is:
The given expression is

49 is the square of 7 and 64 is the square of 8.
So we can write the given expression as


Initial flow rate: 74 gallons/33 minutes = 2.24 gallons/minute
Addtiional flow rate: 2*74/33 = 4.48 gallons/minute
Total new rate: 3*74/33 = 6.72 gallons/minute
The answer is the option C) 6.7