Answer:
(k, -2k+21) where k is any integer
Explanation:
Given the following simultaneous equation;
2x+y=21 ..... 1
y=-2x+21 ..... 2
Subtitute equation 2 into 1:
2x + (-2x+21) = 21
2x -2x+21 = 21
0x = 21-21
0x = 0
x = 0/0
Since the variables cannot be determined, we will subtitute x = k
Substitute x = k into equation 2;
From 2: y = -2x+21
y = -2k+21
Hence the solution to the system of equation is (k, -2k+21) where k is any integer
