Which of the following has four faces?

A.
Icosahedron

B.
Octahedron

C.
Hexahedron

D.
Tetrahedron

Apublic library wants to place 4 magazines and 9 books on each display shelf. the expression 4s+9s represents the total number of items that will be displayed on s shelves. simplify the expression

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

Kelli swam upstream for some distance in a hour.she then swam downstream the same river for the same distance in only 6 minutes.if the river flows at 5km/hr, how fast can kelli swim in still water?