[tex]\displaystyle\bf\\\left \{ {{b_{2} +b_{3} =3} \atop {b_{4} -b_{2} =-1,5}} \right. \\\\\\\left \{ {{b_{1}q+b_{1} q^{2} =3 } \atop {b_{1} q^{3}-b_{1}q=-1,5 }} \right. \\\\\\\left \{ {{b_{1} q(q^{2} -1)=-1,5} \atop {b_{1} q((q+1)=3}} \right. \\\\\\:\left \{ {{b_{1} q(q -1)(q+1)=-1,5} \atop {b_{1} q((q+1)=3}} \right. \\--------------\\q-1=-0,5\\\\q=0,5\\\\b_{1} q(q+1)=3\\\\\\b_{1} =\frac{3}{q(q+1)} =\frac{3}{0,5\cdot(0,5+1)} =\frac{3}{0,5\cdot 1,5} =4\\\\Otvet: \ b_{1} =4[/tex]