Answer:
Step-by-step explanation:
Step 1: y=3x
x+2y=21
Step 2: x+2(3x)=21 (x+6x=21)
Substitute the "y" in the second equation with the "3x."
Step 3: (7x=21)
Combine like terms
Step 4: x=3
Divide
Step 5: y=3(3) or y=9
Plug in your answer to find the value of "y"
