Question 90606
factoring gives (b^2+4)(b^2+9)=0


for b^2+4=0, {{{b=sqrt(-4)}}} and {{{b=-sqrt(-4)}}}, so b=4i and -4i


for b^2+9=0, {{{b=sqrt(-9)}}} and {{{b=-sqrt(-9)}}}, so b=9i and -9i