Answer:
{x,y} = {6,-5}
Step-by-step explanation:
// Solve equation [2] for the variable x
[2] x = 3y + 21
// Plug this in for variable x in equation [1]
[1] (3y+21) + y = 1
[1] 4y = -20
// Solve equation [1] for the variable y
[1] 4y = - 20
[1] y = - 5
// By now we know this much :
x = 3y+21
y = -5
// Use the y value to solve for x
x = 3(-5)+21 = 6
Solution :
{x,y} = {6,-5}
