The sum of three numbers is 51. the second number is 2 times the third. the third number is 9 more than the first. what are the numbers?

X+y+z=51

y=2z

z=9+x

subsitute those

x+2z+9+x=51

x+2 (9+x) + 9+x=51

x+18+2x+9+x=51

4x+27=51

minus 27 both sides

4x=24

divide by 4

x=6

sub back

z=9+x

z=9+6

z=15

y=2z

y=2 (15)

y=30

the numbers are

6,30,15