\[\boxed{\mathbf{55}.}\]
\[1)\ 9200 + 11\ 600 = 20\ 800\]
\[2)\ 8800 + 9200 + 9150 =\]
\[= 18\ 000 + 9150 = 27\ 150\]
\[3)\ 18\ 970 - 9150 = 9\ 820\]
\[4)\ 31\ 820 - 9820 - 11\ 600 =\]
\[= 22\ 000 - 11\ 600 = 10\ 400 -\]
\[в\ апреле.\]
\[11\ 600 - 10\ 400 = 1\ 200 -\]
\[на\ столько\ больше.\]