Consider EIGRP Configured on both routers.
EIGRP decide which link is successor and feasible successor depending on its own parameter calculations.
Parameters include Bandwidth, Delay, Load, Metric, Reliability, and Advertise Distance.
Here are the various situations how EIGRP will select successor and feasible for this scenario.
EIGRP will first calculate Advertise Distance and will select one link as successor which is having lease AD. Incase if AD is equal then we need to consider metric and bandwidth of two links.
Suppose Leased line metric value is lesser than Frame-Realy link metric value then EIGRP will select Leased line as successor and Frame-relay link as feasible successor (Back up link).
Incase if Metric value is also equal then we need to configure Frame-Realy Bandwidth lesser than Leased Line bandwidth to make Frame-Realy as Back up link.