\(39=1\frac{3}{10}b\\----------------------\\1\frac{3}{10}=\frac{1\times10+3}{10}=\frac{13}{10}\\----------------------\\\frac{13}{10}b=39\ \ \ \ |divide\ both\ sides\ by\ \frac{13}{10}=multiply\ boths\ sides\ by\ \frac{10}{13}\\\\b=39\times\frac{10}{13}\\\\b=3\times10\\\\\boxed{b=30}\)
