1. (5 points) Calculate: $0.15 \div 2.1 \times 56=$
【Solution】Solve: $0.15 \div 2.1 \times 56$,
$$
\begin{array}{l}
=0.15 \times 56 \div 2.1 \\
=0.15 \times 8 \times 7 \div 2.1 \\
=1.2 \times \frac{10}{3}, \\
=4 .
\end{array}
$$

Therefore, the answer is: 4 .