RA will use two paths to send the packets: the path from RA through RD to RF and the path from RA through RC and RD to RF. The total cost from RA through RD to RF is 20 + 20 = 40, and the total cost from RA through RC and RD to RF is 10 + 10 + 20 = 40. Open Shortest Path First (OSPF) can load balance traffic across equal-cost paths; since both paths have a total cost of 40, RA can use both paths to send the packets. RA will not always prefer the route through the least number of routers. Instead, RA prefers the intra-area route with the lowest total cost, regardless of the number of routers the packets must pass through.
RA will not use the two paths through Area 0 to send the packets. Although the total cost from RA through both paths is 40, OSPF prefers intra-area routes over inter-area routes, regardless of the total path cost. OSPF uses the following preference order when selecting the best route to a destination:
1. Intra-area routes
2. Inter-area routes
3. External Type 1 routes
4. External Type 2 routes

Therefore, RA prefers an intra-area route with a cost of 40 over an inter-area route with a cost of 40. If all of the routers were within the same area, RA would use all four paths to send the packets.