Noob matrix solving

Hello guys

First time here and giving the first steps on python, so , i started learning this pl 2 weeks ago and they give to me an exercise that i can´t solve or in this case i do not understand

they want

  • matrix[1][3] = 6
  • matrix[3][3] = 12

Matrix = [
[1, 1, 1, 3],
[2, 2, 2, 7],
[3, 3, 3, 9],
[4, 4, 4, 13]

so they requesting the fourth element must be always the sum of first three the hint is using the wrong sums with slicing

i already use import as numpy and

matrix1=([1],[3])
matrix[0]
print(matrix1)
sum(matrix[0])

i cant get it

can you please help ?

thanks a lot