Answer seems to be a straightforward C.

Before rushing to the statements, examine the question stem, and see what pieces of the puzzle you need to answer the question. The question describes an arithmetic series: Each month is x more than the previous month.
For example, if January 2010 plan is 10,000, and x=1,000, then
feb 2010 = 10000+1000 =11000 (previous month +x)
mar 2010 = 11000+1000 = 12000 (previous month + same x)
etc.
Note that it is possible to find the plans for earlier months as well: If i know that oct 2010 is 20000 and x=1000, it is then possible to find previous months by subtracting x:
sep = 20000-1000 = 19000
aug = sep-1000 = 18000
etc.

Thus, in order to find any month next year, you need:
the value of x
the target for a single month (doesn't really matter which) to act as a baseline.

Stat. (1) provides the baseline (december), but not x
Stat. (2) basically tells you that 3x=30,000 (or x=10000), since September is "three jumps of x" more than june:
july is june +x
august = july +x = (june+x)+x = june+2x
sep = aug+x = (june+2x)+x = june+3x.
Thus, both statements are needed to answer the question: mar = dec-9x = 310000-9*10000.

where was your difficulty here? Did you read x taken as a percent, rather than a straightforward addition? Or is the OA something else, and I'm missing something crucial?