420 gallons of 90% antifreeze must be mixed with 60 gallons of 10% antifreeze to get mixture that is 80% antifreeze
<em><u>Solution:</u></em>
Let "x" be the gallons of 90% antifreeze
The, final mixture would contain (x + 60) gallons
Then by given question, we can say,
"x" be the gallons of 90% antifreeze must be mixed with 60 gallons of 10% antifreeze to get 80 % of (x + 60) gallons
<em><u>Thus we frame a equation as:</u></em>
<em><u>Solve the above equation for "x"</u></em>
Thus, 420 gallons of 90% antifreeze is used