Consider the network shown below. The $7$ links have transmission capacities Ri$,$ as shown. The transmission capacities of R$1$ and R$6$ are not given. There are also three sessions $($a$,$b$,$c$)$ from a source $($S$)$ to a destination $($D$)$ traversing these links. The R$7$ link is fairly shared among sessions that are bottlenecked at R$7.$ Suppose that the maximum achievable throughput from Sa to Da is known to be $10$ mbps$,$ and the maximum achievable throughput from Sc to Dc is known to be $30$ mbps$.$ What must the values of R$1$ and R$6$ be in order for these to be the maximum achievable throughputs from Sa to Da and from Sc to Dc$?$ match R$1$ and R$6$ below to values on the right.