Решение:
\[ 1\frac{3}{8} = \frac{1 \times 8 + 3}{8} = \frac{8 + 3}{8} = \frac{11}{8} \]
\[ \frac{11}{8} \times 3 = \frac{11}{8} \times \frac{3}{1} = \frac{11 \times 3}{8 \times 1} = \frac{33}{8} \]
\[ \frac{33}{8} = 33 \div 8 = 4 \text{ (остаток } 1) = 4\frac{1}{8} \]
Ответ: 4⅛