I have interpreted this question differently.
Sheila has 32 coins all together. They are all nickels 5c and dimes 10c. There total value is $250
How many nickels does she have?
Let n be the number of nickels and let d be the number of dimes.
n+d=32 (1)
5n+10d=250 divide through by 5
n+2d=50 (2)
Solve equations 1 and 2 simultaneously. Start with (2)-(1)
$$\begin{array}{rlll}
n+2d&=&50\quad&(2)\\
\underline{n+d}&=&\underline{32}\quad&(1) Now \;subtract\\
d&=&18}
\end{array}\\\\
\begin{array}{rlll}
n+18&=&32\;\; therefore\\
n&=&14
\end{array}\\$$
check 14+18=32 and 5*14+10*18=70+180=250=$250 correct
So Sheila has 14 nickels 
+118741 
