\[a - 3\ \frac{7}{15} = 4\frac{11}{20}\]
\[a = 4\frac{11}{20} + 3\frac{7}{15}\]
\[a = 7\frac{33 + 28}{60}\]
\[a = 7\frac{61}{60} = 8\frac{1}{60}\]
\[Ответ:a = 8\frac{1}{60}.\]