\[\boxed{\mathbf{3.}\mathbf{204}}\]
Пояснение.
Решение.
\[\textbf{а)}\ 24x + 24y = 24 \cdot (x + y)\]
\[x = 32;y = 8:\]
\[24 \cdot (32 + 8) = 24 \cdot 40 = 960.\]
\[\textbf{б)}\ 13a - 13b = 13 \cdot (a - b)\]
\[a = 407;\ \ b = 207:\]
\[13 \cdot (407 - 207) = 13 \cdot 200 =\]
\[= 2600.\]