Look the first question is pretty simple if you look at it
Just eliminate the term 4c from the 2nd and 3rd equation and you get the linear equation in 2 variables which I assume you know how to solve
After finding a and b u can easily find c by putting values in 2 and 3 equation
Problem starts with the second question where you can’t really directly eliminate the third term to form linear equation in 2 variables
So now,
Let’s take 2 equations at a time,
9x - y + z= -28 => 27x - 3y + 3z = -84
3x+2y-3z=-2
Now just add the above equations and you get
30x-y=-86
Similarly take 1st and 3rd equations to find another relation between x and y by eliminating c
Now it has again become to equation two variable in a and b so you can easily find their values