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 $c$ must take for the third equation to hold as well.

\begin{aligned} x + 2 y = a \\ 3 x - y = b \\ 4 x + y = c \end{aligned}