1+r5000+(1+r)2500+(1+r)3500=1+r500+(1+r)2500+(1+r)36000/(1+r)3 - multiply by (1+r)3 provided that r is not equal -1. 1+r5000(1+r)3+(1+r)2500(1+r)3+(1+r)3500(1+r)3=1+r500(1+r)3+(1+r)2500(1+r)3+(1+r)36000(1+r)3 5000(1+r)2+500(1+r)+500=500(1+r)2+500(1+r)+6000 - now cancel out the identical bits on both sides: 5000(1+r)2+500=500(1+r)2+6000 - now get everything on one side of the equation 4500(1+r)2−5500=0 - now you can substitute (1+r) with u and solve this quadratic equation for u (u is not equal to 0)