Given: a+5b is collinear with c,b+6c is collinear with a and a+αb+βc=0.
⇒a+5b=λc...(i)
⇒b+6c=μa...(ii)
⇒a=λc−5b=μb+6c
⇒λc−5b=μ6c+μ1b
Comparing both the sides,
⇒μ=5−1,λ=−30
Putting these values in equation (i)
⇒a+5b=−30c
⇒a+5b+30c=0
Comparing this equation with a+αb+βc=0.
⇒α=5,β=30
⇒α+β=35