Onity Group Project Program Manager interview questions

You have two fuses that take the same amount of time to burn but at different rates at different points in the fuse, and they do not burn at the same rate as each other. Both fuses take 60 minutes to burn each. With an unlimited set of lighters, how do you tell when 45 minutes has elapsed by burning them? You have no way to tell the time other than the fuse(s) burn rate.