How many employees are female who are not members of the custodial staff.

$$Males=\left(\frac{m}{100}\right)\cdot120$$
$$Females=\left(\frac{1-m}{100}\right)\cdot120$$
$$Custodial\ staff=\left(\frac{c}{100}\right)\cdot120$$

Statement 1
m+c= 50; This cannot be related to any of the information provided in the question hence statement 1 is INSUFFICIENT.

Statement 2
The numbers of female employee who are members of custodial staff is four , we don't know total number of female custodial staff hence statement 2 is INSUFFICIENT.

Combining both statement 1 and 2
m + c = 50 ; female custodial staff = 4

None of this information is enough to answer the question, hence both statement together are INSUFFICIENT.

$$answer\ is\ Option\ E$$