How would I calculate this question?

Is that the original question? Because I can't make head or tail of it... :confused:

the sum is equal to 2x + 261 is one possible guess as to what you're asking
261 = 3X squared or X squared = 261... then the equation might be 2x + 3(261) or it might be 261 is the square root of x
all yield different results

Could it be:

Sum of twice a number, added to thrice its square yielding 261?

If so, we can let the number be y.

Then, twice that number becomes 2y, thrice it's square becomes 3y^2.

Or,

2y + 3y^2 = 261

3y^2 + 2y - 261 = 0

Solve the quadratic to get the two possible values of the number.