Let X and Y be the following sums of arithmetic sequences: 
\begin{eqnarray*}X &=& 10+12+14+\cdots+100,\\ Y &=& 12+14+16+\cdots+102.\end{eqnarray*}
What is the value of $Y - X?$
$\textbf{(A)}\ 92\qquad\textbf{(B)}\ 98\qquad\textbf{(C)}\ 100\qquad\textbf{(D)}\ 102\qquad\textbf{(E)}\ 112$
We see that both sequences have equal numbers of terms, so reformat the sequence to look like: 
\begin{align*} Y = \ &12 + 14 + \cdots + 100 + 102\\ X = 10 \ + \ &12 +  14 + \cdots + 100\\ \end{align*}
From here it is obvious that $Y - X = 102 - 10 = \boxed{92 \ \mathbf{(A)}}$.

Note
Another way to see this is to let the sum $12+14+16+...+100=x.$ So, the sequences become
\begin{align*} X = 10+x \\ Y= x+102 \\ \end{align*}
Like before, the difference between the two sequences is $Y-X=102-12=92.$