line_t best_fit(real[] values, int first, int last) {
real sum_x = 0, sum_x2 = 0, sum_y = 0, sum_xy = 0;
int n = last - first + 1;
real m, b;
line_t best_fit(real[] values, int first, int last) {
real sum_x = 0, sum_x2 = 0, sum_y = 0, sum_xy = 0;
int n = last - first + 1;
real m, b;