To find the four solutions of πx + y = 9 we substitute different values for x and y

Let x = 0

Then,

πx + y = 9

(π0) + y = 9

y = 9

(0,9)

Let x = 1

Then,

πx +y = 9

(π×1)+y = 9

π+y = 9

y = 9-

(1, 9-)

Let y = 0

Then,

πx+y = 9

πx+0 = 9

πx = 9

x = 9/

(9/,0)

Let x = -1

Then,

πx + y = 9

(×-1) + y = 9

- + y = 9

y = 9+π

(-1,9+)

The solutions are (0,9), (1,9-), (9/,0), (-1,9+)