Step 1: Least squares for a line through the origin.
Minimizing \(S(m)=\sum(y_i-mx_i)^2\) gives \(m = \dfrac{\sum x_iy_i}{\sum x_i^2}\).
Step 2: Tabulate.
\(x_iy_i\): 2, 12, 21, 40; sum = 75. \(x_i^2\): 1, 4, 9, 16; sum = 30.
Step 3: Compute m.
\[ m = 75/30 = 2.5 \]
\[ \boxed{m = 2.5} \]