Question 992663
Check how this example was done and you should be able to solve your exercise :


<a href="https://www.youtube.com/watch?v=-REjxT9KCzQ">two part mixture, percents, using just a single variable</a>
Just identify carefully which numbers are known and which are unknown to be solved.


Actually, your exercise has only one unknown material, so the equation to setup would be this:
{{{(v*80+60*17)/(v+60)=70}}}
and v is the volume of the 80% acid to add.