Let me show you how I did it,

The matrix,

A is 3 rows 2 colums.

Matrix (vector) b is 2 rows 1 colums

Thus,

X is 1 row 2 coloms.

That means,

X=[x,y]

For some numbers x and y.

But,

AX=([x +3y],[2x+y],[7x+2y])

Thus, by equality,

x+3y=1

2x+y=2

7x+2y=3

Solving the first two equations we have,

y=0 and x=1

But,

That does not solve the third equations.

There there is no such coefficient matrix X.