Question 305287
Let A be the number of gallons of 100% acid that gets added.
{{{69+7/9=628/9}}}
Write the concentration equation for the mixture,
{{{100*A+32*8=(628/9)(A+8)}}}
Multiply both side by 9.
{{{900A+2304=628A+5024}}}
{{{272A=2720}}}
{{{A=10}}}
Add 10 gallons of 100% acid.