Question 235169
Does {{{N}}} stand for nickels? If so,
{{{Q = 5}}}
{{{D = 2Q}}}
There are {{{16}}} coins in all, so 
{{{Q + D + N = 16}}}
Now I can do substitutions
{{{Q + 2Q + N = 16}}}
{{{3Q + N = 16}}}
And,since {{{Q = 5}}}
{{{3*5 + N = 16}}}
{{{15 + N = 16}}}
Subtract {{{15}}} from both sides
{{{N = 1}}}
Therefore,
{{{Q = 5}}}
{{{D = 10}}}
{{{N = 1}}}