Let $\mathbf{U}$ be any point on the graph of $y=3 x^2$, and let $\mathbf{S}$ and $\mathbf{T}$ be the (perpendicular) projections of $\mathbf{U}$ on the $x$ - and $y$-axes, respectively. Find an equation for the locus of the point $\mathbf{Q}$ on $\overline{\mathbf{S T}}$ that lies one-third of the way from $\mathbf{S}$ to $\mathbf{T}$. [Hint: Draw a sketch similar to the one for Exercise 20.]