What is the percentage change in the backlog for Cubic Mission Solutions in 2019?
{"": {"September 30,   ": 2019.0, "September 30,    ": 2018.0}, "Total backlog     -- Cubic Transportation Systems": {"September 30,   ": 2953.3, "September 30,    ": 3544.9}, "Total backlog     -- Cubic Mission Solutions": {"September 30,   ": 103.7, "September 30,    ": 77.0}, "Total backlog     -- Cubic Global Defense": {"September 30,   ": 344.0, "September 30,    ": 442.6}, "Total backlog     -- Total  ": {"September 30,   ": 3401.0, "September 30,    ": 4064.5}}
total_backlog_2019 = df["Total backlog     -- Cubic Mission Solutions"]["September 30,   "]
total_backlog_2018 = df["Total backlog     -- Cubic Mission Solutions"]["September 30,    "]
answer = ( total_backlog_2019 - total_backlog_2018 ) / total_backlog_2018 * 100.0