Answer:
She should add 18 liters of 30% sugar syrup
Step-by-step explanation:
Let the amount of sugar syrup be x
Mathematically;
30% of x liters + 20% of 12 liters = 26% of (x + 12)
So, we have
0.3x + 2.4 = 0.26x + 3.12
0.3x-0.26x = 3.12-2.4
0.04x = 0.72
x = 0.72/0.04
x = 18