Midpoint of diagonal AC is M=(−1,−2). Slope of AC=−3−1−6−2=2.
In a rhombus, diagonals are perpendicular bisectors. So BD has slope −21 and passes through M: y+2=−21(x+1).
AD has slope 7: γ−1δ−2=7⇒δ=7γ−5.
D lies on BD: δ=−2γ−25.
Solving: 7γ−5=−2γ−25⇒γ=31, δ=−38.
B=(2(−1)−31,2(−2)+38)=(−37,−34).
∣α+β+γ+δ∣=−37−34+31−38=∣−6∣=6.