herp derp herp derp herp derp
We can figure this out using the explicit formula.

n represents the term we are looking for.
f(1) represents the first term in the sequence, which in this case, is 7.
d represents the common difference, which in this case, is +3.
f(n) = 7 + 3(n - 1)
f(n) = 7 + 3n - 3
f(n) = 4 + 3n
Now, we can input 214 for n and solve.
f(214) = 4 + 3(214)
f(214) = 4 + 642
f(214) = 646
The 214th term in this sequence is 646.
Answer: 7(3m - 7n)
<u>Step-by-step explanation:</u>
Factor each term then see what value(s) they have in common:
21m - 49n
∧ ∧
3 · 7 · m 7 · 7 · n
Both terms have a 7 in common. What is left over after removing the 7?
21m: 7(3m)
49n: 7(7n)
GCF: 7 Leftovers: 3m <em>and</em> 7n
Factored form of expression is: 7(3m - 7n)