x ∑xN
15 = ∑xN
∑x = 15N........(i)
y = ∑yNy=∑x+45N+1
181=15N+45N+1
18(N + 1) = 15N + 45
18N + 18 = 15N + 45
18N - 15N = 45 - 18
3N = 27
N = 273
= 9