TIMO - 2019 - Grade 9 - Heat Round - Paper 3 Question 9

Find $t$ in $\begin{cases}r+s+t+u+4v=18\\r+s+t+4u+v=19\\r+s+4t+u+v=20\\4r+s+t+u+v=21\\r+4s+t+u+v=22\end{cases}$.