Put all the each x and y pair on a row. Formulate the matrix A containing all the x1...x81 and x values. Put the y values in a column matrix. Use backslash to linear least squares solve.
assume each column of x is x1, x2, etc and each row is a point.
A = [x(:,1) x(:,2) ... x(:,81)] in other words, A = x
a = A\y
Note, there is a lot of issues related to stability of this problem. Research linear least squares problem. This is a good place to start: Systems of Linear Equations
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