Arrestin binds to a phosphorylated ligand$-$receptor complex, blocking the binding and activation of G$-$proteins, according to the following reaction: $+1+1$ Arrestin binds reversibly with LR with a dissociation constant of $=/,$ in units of molecules per cell. Only free LR can bind to G$-$proteins. A balance on LR yields $=+$ To determine the effect of arrestin on G$-$protein activation, the experiment described above for Problem $2$ was repeated in the absence of the drug that inhibits arrestin biniding