TMUA Specimen Paper 1 Question 12

The cross-section of a triangular prism is an equilateral triangle with side $2x$ cm. The length of the prism is $d$ cm. Let the total surface area of the prism be $T$ cm${}^2$. Given that the volume of the prism is $T$ cm${}^3$, which one of the following is an expression for $d$ in terms of $x$?