Which expression has a value of 15, using only four 4s and any of the following: + , – , · , ÷, exponents, and/or parentheses

If you had $1,900,000, how many days would it take you to spend all if you spent $1 a second. (there are 86,400 seconds in a day)

I'm confused on this could anyone me and show me what i need to do to solve it.

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