\[\boxed{\mathbf{3.}\mathbf{29.ОК\ ГДЗ - домашка\ на\ }5}\]
\[\textbf{а)}\ 5a + 650\]
\[a = 13:\]
\[5 \cdot 13 + 650 = 65 + 650 = 715.\]
\[a = 15:\]
\[5 \cdot 15 + 650 = 75 + 650 = 725.\]
\[\textbf{б)}\ 16(b - 13)\]
\[b = 13:\]
\[16(13 - 13) = 16 \cdot 0 = 0.\]
\[b = 28:\]
\[16(28 - 13) = 16 \cdot 15 = 240.\]