TeX source:

\begin{array}{l} 3(2+5)=\underbrace{2+5+2+5+2+5}_{2+5 \text { appears } 3 \text { times }}\\ 3(2+5)=\underbrace{2+2+2}_{2 \text { appears } 3 \text { times }}+\underbrace{5+5+5}_{5 \text { appears } 3 \text { times }}\\ \begin{array}{l} 3(2+5)=3 \cdot 2+3 \cdot 5 \\  \quad \qquad \qquad 3 \times 2 \quad 3 \times 5 \end{array} \end{array}