A box contains $R$ red balls, $B$ blue balls, and no other balls. One ball is removed and set aside, and then a second ball is removed. On each draw, each ball in the box is equally likely to be removed. The probability that both of these balls are red is $\frac{2}{7}$. The probability that exactly one of these balls is red is $\frac{1}{2}$. Determine the pair $(R, B)$.