Question 64036
n = number of nickels
q = number of quarters
{{{n = q + 7}}} given   
{{{5n + 25q = 125}}} given
multiply both sides of 1st by 5
{{{5n - 5q = 35}}} now subtract
{{{-5n - 25q = -125}}}
{{{-30q = -90}}}
{{{q = 3}}}
{{{n = q + 7}}}
{{{n = 3 + 7}}}
{{{n = 10}}}
He has 3 quarters and 10 nickels
check
{{{5n + 25q = 125}}}
{{{5*10 + 25*3 = 125}}}
{{{50 + 75 = 125}}}
{{{125 = 125}}}
OK