[tex]\displaystyle\bf\\\left \{ {{b_{3} +b_{4}=36 } \atop {b_{2} +b_{3} =18}} \right. \\\\\\\left \{ {{b_{1} q^{2} +b_{1} q^{3} =36} \atop {b_{1} q+b_{1} q^{2} =18}} \right. \\\\\\:\left \{ {{b_{1} q^{2} (1+q)=36} \atop {b_{1} q(1+q)=18}} \right. \\-----------\\q=2\\\\b_{1} q(1+q)=18\\\\\\b_{1} =\frac{18}{q(1+q)}=\frac{18}{2\cdot3} =3\\\\\\b_{5} =b_{1}\cdot q^{4} =3\cdot 2^{4}=3\cdot16=48\\\\\\Otvet: \ b_{1} =3 \ , \ b_{5} =48[/tex]