A matrix method is far simpler I suppose:

h x 3     2    1
1   ⌈3    2    1 ⌉
-2  |-6  -4   -2|
 3  ⌊9    6    3 ⌋

Now just add up the diagonals:

y[0] = 3
y[1] = -4
y[2] = 6
y[3] = 4
y[4] = 3

p.s I don't know how to type in a matrix here.

A matrix method is far simpler I suppose:

h  x   x1      x2      x3
h1  ⌈x1*h1   x2*h1    x3*h1 ⌉
h2  |x1*h2   x2*h2    x3*h2|
h3  ⌊x1*h3   x2*h3    x3*h3 ⌋

h x 3     2    1
1   ⌈3    2    1 ⌉
-2  |-6  -4   -2|
 3  ⌊9    6    3 ⌋

Now just add up the diagonals:

y[0] = 3
y[1] = -4
y[2] = 6
y[3] = 4
y[4] = 3

p.s I don't know how to type in a matrix here.