Statement 1: Here b will have 3 as one of its multiples. For x to be a multiple of 9 we need another 3. If c is 3 or any multiple of 3, then x will be a multiple of 9. Otherwise x will not necessarily be a multiple of 9. - INSUFFICIENT
Statement 2: If c is less than 4, c may or may not be a multiple of 9. For instance, if c=-9, then x will be a multiple of 9, otherwise not necessarily. - INSUFFICIENT
Combining both statements together, we can find out that x is a multiple of 9. Hence, C.