Hello Stephen

Welcome to Math Help Forum!Suppose he uses cc of the first solution, and cc of the second. Then we can set up two simultaneous equations as follows:

The total volume must be 20 cc. Therefore

?This is equation (1).

The quantity of the medicine in cc of the first solution is .

The quantity of the medicine in cc of the second solution is .

The total quantity of medicine in the mixture is therefore ... ?

This must be 6% of the total volume, cc, which is ?

The second equation is therefore

?This is equation (2).

Can you complete what I have started, and then solve the simultaneous equations to find and ?

Grandad