The general form of the equation of a circle is,
x² + y² + Dx + Ey + F = 0, where D, E, F are constants.
The given equation is 7x² + 7y² − 28x + 42y − 35 = 0. So, to convert this equation into a general form we just need to get rid of the leading coefficient 7.
Hence, divide both sides of the equation by 7. So,

x² + y² − 4x + 6y − 5=0.
So, the general form of the equation is x² + y² − 4x + 6y − 5=0.
Answer: the value of x is 45
Step-by-step explanation: its a little bit bigger than the 40 on the right
Answer:

Step-by-step explanation:
we know that
A relationship between two variables, x, and y, represent a direct variation if it can be expressed in the form
or 
In this problem
Let
x------> the number of gallons
y------> the number of miles
the relationship between the number of miles and the gallons of gas represent a linear direct variation
The constant of proportionality k is equal to the slope m

therefore
the equation of the linear equation

You have to isolate x. First you start off by adding the like terms which is -3x and -x. By adding them you get -4x.
8 - 4x = 12
Then you subtract 8 on both sides since it is positive to isolate x.
-4x = 4
Then you divide -4 by both sides and get x=4/-4
4/-4 is simplified to -1 so the answer is x= -1