I need help please include explanations thank you

Which ordered pair (c,d) is a solution to the given system of linear equations- c+2d=13 -9c-4d=-15

Complete the steps to find 4.830 ÷ 5

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