the distance of the line 3x - y = 6 and P (1, 2)

my attempt : A = 3, B = - 1, C = -6,

d = 3(1) + (-1)(2) - 6/ sq. rt. 3^2 + -1^2

i arrived at sq. rt of 10/ 2.... is this correct? because im so confused when the book's answer is (5/2) sq. rt of 10

i dont know which of this is correct answer. i followed the formula already but they dont have the same answer.