Let:
x = mL of soda solution
y = mL of syrup solution
The soda solution is 80% strength and the syrup solution is 0% strength, thus the combination of x and y of each solution gives strength of:
80x + 0y
This combination must be 60% strength, thus:
80x + 0y = 60(x + y) [1]
The total amount of solution is 65 mL, thus:
x + y = 65
Substituting in [1]
80x + 0y = 60*65
Operating and simpliifying:
80x = 3900
Dividing by 80:
x = 48.75
I need 48.75 mL of soda solution