Orthogonality & Least Squares · Medium problem

A calibration gives two equations for the same quantity $s$: $s = 3$ and $2s = 7$, which are inconsistent. The matrix of coefficients, $\begin{pmatrix}1\\2\end{pmatrix}$, has rank $1$, so only $s$ itself (not separate unknowns) can be estimated. Find the least-squares estimate of $s$.