Let us assume the unknown number = x
Now we have to follow the details given in the question to bring out the actual equation. In this case there will be only one equation.
(x/3)^2 - (2x + 7) = 0
(x/3)^2 = 2x + 7
x^2/9 = 2x + 7
x^2 = 9(2x + 7)
x^2 = 18x + 63
x^2 - 18x = 63
This would be the final equation for the given problem. his problem needs any solver to understand the words very minutely.