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Divide 999 by 7:
\div 7 \approx 142.7143
The largest integer less than or equal to 142.7143 is 142.
So, the largest 3-digit multiple of 7 is:
\times 142 = 994
Now, the sequence of 3-digit multiples of 7 is:
105, 112, 119, \dots, 994
This is an arithmetic sequence with first term \(a = 105\), common difference \(d = 7\), and last term \(l = 994\).
The number of terms \(n\) is given by:
l = a + (n - 1)d