What primary static route should be configured on R1, to ensure backup routing occurs (and the primary static route is removed) if the primary link between R1 and R2 fails?

Refer to the Exhibit. Routers R1 and R2 are connected by two links, one primary (1.544Mbps) and one backup (512Kbps). For this network design, the backup link should only be used if the primary link is down, and it was decided only static routing be used. Therefore, a default route to the Internet and two static routes pointing to the 172.16.1.0/24 network are to be configured on R1. What primary static route should be configured on R1, to ensure backup routing occurs (and the primary static route is removed) if the primary link between R1 and R2 fails?