for solving we have to make A & B as same
so 8x+6y−30=0 ( taking 2 common) becomes 4x+ 3y-15
then using eqn c1-c2)/root of A^2+b^2
c1= 5, c2=-15, A=4, B=3
solving, (5-(-15))/root of 4^2+3^2=(5+15)/root of 4^2+3^2
=20/root of 25= 20/5=4
hence the answer. any doubt please let me know
regards