x int can be found by subbing in 0 for y and solving for x
9x - 7y = 21
9x - 7(0) = 21
9x = 21
x = 21/9 which reduces to 7/3...so the x int is 7/3 or (7/3,0) <==
to find the y int, sub in 0 for x and solve for y
9x - 7y = 21
9(0) - 7y = 21
-7y = 21
y = -21/7
y = -3....so the y int is -3 or (0,-3) <==