and i don't know what to do from there. text book is really horrible.
You have four equations in four unknowns: x+ y= 3, x+ z= 5, y+ z= 5 and w= 4.
If you subtract the third equation from the second, you eliminate z: x+ z- (y+ z)= x- y= 0.
Can you solve the two equations x+ y= 3 and x- y= 0?