Subtract seven more than twice a number from the square of one-third of the number you get zero

X=the number
the square of 1/3 the number = (x/3)^2 = (x^2)/9
7 more than twice the number=2x+7
2x+7- ((x^2)/9)=0
2x+7 = (x^2)/9
multiply both sides by 9:
18x+63=x^2
subtract 18x+63 from both sides:
x^2-18x-63=0
you can use the quadratic formula or factor it as 
(x-21)(x+3)=0
the number is -3 or 21

1/3squared(2x+7)=0
1/9(2x+7)=0
2/9x+7/9=0
2/9x=-7/9
x=-7/2 or -3 and 1/2