Algebra 2ChallengeSystems of Equations

Systems of Equations · Challenge problem

Three equations, only two unknowns. Solve the first two for $x$ and $y$ , then give the value $u$ must take for the third equation to hold as well.

\begin{aligned} x - 4 y = s \\ 3 x + 2 y = t \\ 2 x + y = u \end{aligned}