Last Algebraic Sentence.

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

Let N be the number.....

"Seven more than twice a number"  ⇒     2N + 7      (1)

"Square of 1/3 of the number" ⇒   (N/3)^2         (2)

So....we are subtracting  (1) from (2)   and this = 0        .....so....

(N / 3)^2  -  [ 2N + 7]  =   0

(1/3 x)^2  -(7+ 2x) = 0