In general, the air temperature decreases 12 degrees fahrenheit for every 4,000 feet increase altitude. if a hiker climbs 3,000 feet, by how much can she expect the temperature to increase?

9 degrees

because 12/4 = 3 degrees (per 1000 feet)
3 x 3 = 9 degrees total (in 3000 feet)

hope this helps

It's like discovering the answer to a puzzle. the purpose in solving an equation is to find the value or values of the variable that makes it a true statement. any value of the variable that makes the equation true is called a solution to the equation.