**Concept: The question tests on the application of basic arithmetic in a Word problem format.**

**Solution:**

St (1)

Given – There is an additional 30 minutes of use (450-420=30) and

T = 13,755

Thus 13755 = F + 30 M

We do not know F and hence we cannot compute the value of M. **(Insufficient)**

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St (2) - Given T= 13,125 and since used minutes is less than 420,the value of x=0 (additional minutes)

Hence 13125 = F + 0

- F = 13125

However the value of M cannot be computed as x = 0. **(Insufficient)**

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On combining both, we have

13755 = 13125 +30 M

M can be computed (Sufficient)

Hence **option (C)**

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