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

ryan had a head start of 10 meters.