The circumference is times diameter. So one rotation of the pedals will cause the front chain drive to complete one full turn, so it will move the chain the same distance as it's circumference. So it will move the chain inches. Then the back drive has a circumference of inches, but it only turns inches. So it turns of a full rotation. Since the wheel turns at the same rate as the back chain drive, the wheel will turn of a full turn as well. And since the back wheel is 26 inches in diameter, it's circumference is inches. If it turned a full rotation, it would go this distance along the ground, but it is only giong of this distance, so it is going inches. Or approximately 59.8997 inches.

...unless I misunderstood.