Is anyone willing enough to answer this question

What percent of the circle below is shaded?

How do you find the circumfrance of a circle?

Serena is making an experiment. for that, she needs 20 grams of a 52% solution of salt. she has two large bottles of salt water: one with 40% and the other with 70% of salt in them. how much of each must she use to make the solution she needs? i am in need of