What is the answer to this question ?

If x is 6, then 7x= a. 13 b. 42 c. 42x d. 76

What percent of 18 is 24? and plz explain thx.

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