Question 570138
x+y=9.........(1)
y=2x........(2)
Put value of y from (2) to (1)

x+y=9
x+2x=9
3x=9
3x/3=9/3
x=3...............(3)
Put the value of x in (2)

y=2x
y=2(3)
y=6

x,y=3,6



Check
Put the value of x and y in (1)
x+y=9.........(1)
3+6=9
9=9
Put the value of x and y in (2)
y=2x
6=2(3)
6=6