$\begin{aligned}[t] p + 2q &= 7\\ 3p + 4q &= 11 \end{aligned}$ 

$\begin{aligned}[t] 4m − 5n &= −2\\ {-}3m + 4n &= 9 \end{aligned}$ 

$\begin{aligned}[t] 4x − y + z &= −5\\ 2x + 2y + 3z &= 10\\ 5x − 2y + 6z &= 1 \end{aligned}$ 

$\begin{aligned}[t] 7w − 3x + 2z &= 41 \\ −2w + x − z &= −13 \\ 4w + y − 2z &= 12\\ x − 3z & = 1 \end{aligned}$