ok question about matrix and regression the problem is how do i calculate this, i know how to calculate matrixs but i have no idea how to or even where too start using a matrix built from regression.

y=xb+u
y1 1..x11.... x21 u1
y2= 1..x12... x22 bo u2
y2 1..x13...x23 b1 u3
y3 1...x14..x24 b2 u4
y4 1...x15...x24 u5