{b1+b2=108 {b2+b3=135 {b1+b1*q=108 {b1*q+b1*q^2=135 {b1(1+q)=108, b1=108/(1+q) {b1q(1+q)=135 108q(1+q)/(1+q)=135 108q=135 q=1,25 b1=108/(1+1,25)=48 b2=b1*q=48*1,25=60 b3=b2*q=60*1,25=75 48, 60, 75