A "linear combination" of objects x, y, z (vectors, equations, or anything you can add and multiply by numbers) is ax+ by+ cy where a, b, and c are numbers. You are asked to find three numbers a, b, and c, such that a(u+ v+ w)+ b(u+ 2v+ 3w)+ c(v+ 2w)= 0. Of course, you would do the same on the right and have 0= 2a+ b. The problem is telling you that you should find that 2a+ b= 1. If you were to replace that 0 with x, then you would have 2a+ b+ cx. What should x be so 2a+ b+ cx= 0?

Again, a linear combination is simply sums of numbers times the objects, in this case the columns of the matrix. That is, if the matrix isWrite the system in a column picture. Show that the three columns on the left lie in the same plane by expressing the third column as a combination of the first two. WHat are all the solutions (u,v,w) if the column on the right side of the equation is changed to (0,0,0)?

then a "linear combination" of the columns are

for number x, y, and z.

I am concerned about your apparent ignorance of basic definitions. Whoever gave you these exercises clearly expects you to know what a "linear combination" is!