(Statistical Inference) Given the following model,

yi = ₁+ ₂ x_i + ₃ z_i + _i

I have collected data and computed the following moment matrix with M = [1, x, z, y] for you:

| 120 150 80 450 |

| 150 300 250 2000 |

| 80 250 600 1200 |

| 450 2000 1200 25000 |

How many observations have I collected? What are the average values for each variable, that is y, x, and z?