Question 570850
these are fun questions, brings me back to learning to count with money..anyway
dimes(d) and quarters(q) 
given
dimes are worth .10 and quarters are worth .25
{{{.10(d)+.25(q)=19.75}}}
{{{d+q=100}}}
.
to solve for (d) you must substitute for (q)
{{{q=highlight(100-d)}}}
{{{.10(d)+.25(q)=19.75}}}
{{{.10(d)+.25(highlight(100-d))=19.75}}}
{{{.10d+25-.25d=19.75}}}
{{{25-.15d=19.75}}}
{{{25=19.75+.15d}}}
{{{25-19.75=.15d}}}
{{{5.25=.15d}}}
{{{highlight(35=d)}}}