Explanation:
Lets FOIL it out:
6+4i+3bi+2bi²=13i
6-4i-13i+3bi+2bi²=0
6-9i+3bi+2bi²=0,but i²=-1
3bi-2b=9i-6
b(3i-2)=9i-6
Divide both sides by (3i-2)
b=(9i-6)/(3i-2)
Rationalize the expression by multiplying through by the conjugate of (3i-2) which is (3i+2)
b=(27i²+18i-18i-12)/(9i²+6i-6i-4),again i²=-1
b=27i²-12/9i²-4
b=-27-12/-9-4
b=-39/-13
b=3