Question 548261
Let q be the number of quarters and n be the number of nickels.  From the question we know that 
{{{q=2n}}}       (1)
and 
{{{25q+5n=825}}}    (2)
(Note:   I had to change 8.25 to cents so everything was measure in the same units... as well I used 25 for q since quarters are 25 cents and 5 for n as nickels are worth 5 cents.)


Now we can substitute (1) into (2) and solve for n.  This leaves:
{{{25(2n)+5n=825}}}
{{{50n+5n=825}}}
{{{55n=825}}}
{{{n=825/55}}
{{{n=15}}}

Now we know we have 15 nickels... to find the number of quarters we have, we must substitute this number of nickels back into equation (1) and solve for q.  I will leave this next part to you..

Let me know if you are unsure about anything:)