In the system 4x + 9y = 7 and and 4x - 9y = 9, would I add or subtract this system to solve for x? To solve for y?

add to solve for x or add to solve for y

subtract to solve for x or subtract to solve for y

add to solve for x and subtract to solve for y

subtract to solve for x and add to solve for y

add to solve for x and subtract to solve for y

Step-by-step explanation:

To solve for any variable, it is required to eliminate the other variable in two variable - two equation set.

The set of equations are

4x + 9y = 7  1

4x - 9y = 9 2

To solve for x we need to eliminate  Y

We see that in equation 1 there is 9y and

in equation 2 there is -9y

if we add 9y and -9y (9y -9y = 0)

Hence it is clear  that to solve for x , it is needed to add equation 1 and equation 2.

by adding equation 1 + equation 2 we have

4x + 9y = 7  1

=> 4x - 9y = 9 2

=>4x + 9y + 4x -9y  = 7 +9

=>8x = 16

=>x = 16/8 = 2

To solve for y we need to eliminate  x

We see that in equation 1 there is 4x and

in equation 2 also there is 4x

if we subtract 4x and 4x (4x -4x= 0) , we get 0

Hence it is clear  that to solve for y , it is needed to subtract equation 2 from equation 1.

by performing equation 1 - equation 2 we have

4x + 9y = 7  1

=> 4x - 9y = 9 2

=>4x + 9y -( 4x -9y)  = 7 - 9

=>4x + 9y - 4x +9y  = -2

=>18y = -2

=>y =  -2/18 = -1/9

Thus, correct answer is

add to solve for x and subtract to solve for y

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.