3x + y = 21 --- (1)
2x - 7y = -9 --- (2)
From (1), we have:
y = -3x + 21 --- (3)
Substituting (3) into (2), we will get:
2x - 7(-3x + 21) = -9
2x + 21x - 147 = -9
23x = 147 - 9
23x = 138
x = 138 / 23
x = 6
Substituting x = 6 into (3), we will get:
y = -3(6) + 21
y = -18 + 21
y = 3
Hence, x = 6 and y = 3