\[\boxed{\mathbf{1.}}\]
\[\textbf{а)}\ 4\ 052\ 300 =\]
\[= 4\ 000\ 000 + 50\ 000 + 2000 + 300\]
\[\textbf{б)}\ 4\ 052\ 299\]
\[\boxed{\mathbf{2.}}\]
\[\textbf{а)}\ 45 + 17 = 62\]
\[\textbf{б)}\ 57\ :19 = 3\]
\[\textbf{в)}\ 80 - 18 \cdot 4 = 80 - 72 = 8\]
\[\boxed{\mathbf{3.}}\]
\[\boxed{\mathbf{4.}}\]
\[= 44 - 1 + 0 + 5 = 48\]
\[\boxed{\mathbf{5.}}\]
\[16 - 9 = 7 \cdot 8 = 56 + 4 =\]
\[= 60\ :5 = 12\]
\[Ответ:\]
\[Лена\ задумала\ число\ 12.\]